/* http_proxy.c - HTTP proxy support functions
 *
 * Copyright (c) 1994-2011 Carnegie Mellon University.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 *
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in
 *    the documentation and/or other materials provided with the
 *    distribution.
 *
 * 3. The name "Carnegie Mellon University" must not be used to
 *    endorse or promote products derived from this software without
 *    prior written permission. For permission or any legal
 *    details, please contact
 *      Carnegie Mellon University
 *      Center for Technology Transfer and Enterprise Creation
 *      4615 Forbes Avenue
 *      Suite 302
 *      Pittsburgh, PA  15213
 *      (412) 268-7393, fax: (412) 268-7395
 *      innovation@andrew.cmu.edu
 *
 * 4. Redistributions of any form whatsoever must retain the following
 *    acknowledgment:
 *    "This product includes software developed by Computing Services
 *     at Carnegie Mellon University (http://www.cmu.edu/computing/)."
 *
 * CARNEGIE MELLON UNIVERSITY DISCLAIMS ALL WARRANTIES WITH REGARD TO
 * THIS SOFTWARE, INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
 * AND FITNESS, IN NO EVENT SHALL CARNEGIE MELLON UNIVERSITY BE LIABLE
 * FOR ANY SPECIAL, INDIRECT OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN
 * AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING
 * OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 *
 */

#include <config.h>

#ifdef HAVE_UNISTD_H
#include <unistd.h>
#endif
#include <assert.h>
#include <ctype.h>
#include <syslog.h>
#include <sasl/sasl.h>
#include <sasl/saslutil.h>

#include "httpd.h"
#include "http_proxy.h"
#include "iptostring.h"
#include "mupdate-client.h"
#include "prot.h"
#include "proxy.h"
#include "spool.h"
#include "tls.h"
#include "tok.h"
#include "version.h"
#include "xmalloc.h"
#include "xstrlcat.h"
#include "xstrlcpy.h"

/* generated headers are not necessarily in current directory */
#include "imap/http_err.h"
#include "imap/imap_err.h"

#include <libxml/uri.h>

static int login(struct backend *s, const char *userid,
                 sasl_callback_t *cb, const char **status,
                 int noauth);
static int ping(struct backend *s, const char *userid);
static int logout(struct backend *s __attribute__((unused)));


HIDDEN struct protocol_t http_protocol =
{ "http", "HTTP", TYPE_SPEC,
  { .spec = { &login, &ping, &logout } }
};


EXPORTED const char *digest_recv_success(hdrcache_t hdrs)
{
    const char **hdr = spool_getheader(hdrs, "Authentication-Info");

    return (hdr ? hdr[0]: NULL);
}


static const char *callback_getdata(sasl_conn_t *conn,
                                    sasl_callback_t *callbacks,
                                    unsigned long callbackid)
{
    sasl_callback_t *cb;
    const char *result = NULL;

    for (cb = callbacks; cb->id != SASL_CB_LIST_END; cb++) {
        if (cb->id == callbackid) {
            switch (cb->id) {
            case SASL_CB_USER:
            case SASL_CB_AUTHNAME: {
                sasl_getsimple_t *simple_cb = (sasl_getsimple_t *) cb->proc;
                simple_cb(cb->context, cb->id, &result, NULL);
                break;
            }

            case SASL_CB_PASS: {
                sasl_secret_t *pass;
                sasl_getsecret_t *pass_cb = (sasl_getsecret_t *) cb->proc;
                pass_cb(conn, cb->context, cb->id, &pass);
                result = (const char *) pass->data;
                break;
            }
            }
        }
    }

    return result;
}


#define BASE64_BUF_SIZE 21848   /* per RFC 2222bis: ((16K / 3) + 1) * 4  */

static int login(struct backend *s, const char *userid,
                 sasl_callback_t *cb, const char **status,
                 int noauth __attribute__((unused)))
{
    int r = 0;
    socklen_t addrsize;
    struct sockaddr_storage saddr_l, saddr_r;
    char remoteip[60], localip[60];
    static struct buf buf = BUF_INITIALIZER;
    sasl_security_properties_t secprops =
        { 0, 0xFF, PROT_BUFSIZE, 0, NULL, NULL }; /* default secprops */
    const char *mech_conf, *pass, *clientout = NULL;
    struct auth_scheme_t *scheme = NULL;
    unsigned need_tls = 0, tls_done = 0, auth_done = 0, clientoutlen;
    hdrcache_t hdrs = NULL;

    if (status) *status = NULL;

    /* set the IP addresses */
    addrsize = sizeof(struct sockaddr_storage);
    if (getpeername(s->sock, (struct sockaddr *) &saddr_r, &addrsize) ||
        iptostring((struct sockaddr *) &saddr_r, addrsize, remoteip, 60)) {
        if (status) *status = "Failed to get remote IP address";
        return SASL_FAIL;
    }

    addrsize = sizeof(struct sockaddr_storage);
    if (getsockname(s->sock, (struct sockaddr *) &saddr_l, &addrsize) ||
        iptostring((struct sockaddr *) &saddr_l, addrsize, localip, 60)) {
        if (status) *status = "Failed to get local IP address";
        return SASL_FAIL;
    }

    /* Create callbacks, if necessary */
    if (!cb) {
        buf_setmap(&buf, s->hostname, strcspn(s->hostname, "."));
        buf_appendcstr(&buf, "_password");
        pass = config_getoverflowstring(buf_cstring(&buf), NULL);
        if (!pass) pass = config_getstring(IMAPOPT_PROXY_PASSWORD);
        cb = mysasl_callbacks(NULL, /* userid */
                              config_getstring(IMAPOPT_PROXY_AUTHNAME),
                              config_getstring(IMAPOPT_PROXY_REALM),
                              pass);
        s->sasl_cb = cb;
    }

    /* Create SASL context */
    r = sasl_client_new(s->prot->sasl_service, s->hostname,
                        localip, remoteip, cb, SASL_USAGE_FLAGS, &s->saslconn);
    if (r != SASL_OK) goto done;

    r = sasl_setprop(s->saslconn, SASL_SEC_PROPS, &secprops);
    if (r != SASL_OK) goto done;

    /* Get SASL mechanism list.  We can force a particular
       mechanism using a <shorthost>_mechs option */
    buf_setmap(&buf, s->hostname, strcspn(s->hostname, "."));
    buf_appendcstr(&buf, "_mechs");
    if (!(mech_conf = config_getoverflowstring(buf_cstring(&buf), NULL))) {
        mech_conf = config_getstring(IMAPOPT_FORCE_SASL_CLIENT_MECH);
    }

    do {
        unsigned code;
        const char **hdr, *errstr, *serverin;
        char base64[BASE64_BUF_SIZE+1];
        unsigned int serverinlen;
        struct body_t resp_body;
#ifdef SASL_HTTP_REQUEST
        sasl_http_request_t httpreq = { "OPTIONS",      /* Method */
                                        "*",            /* URI */
                                        (u_char *) "",  /* Empty body */
                                        0,              /* Zero-length body */
                                        0 };            /* Persistent cxn? */
#endif

        /* Base64 encode any client response, if necessary */
        if (clientout && scheme && (scheme->flags & AUTH_BASE64)) {
            r = sasl_encode64(clientout, clientoutlen,
                              base64, BASE64_BUF_SIZE, &clientoutlen);
            if (r != SASL_OK) break;

            clientout = base64;
        }

        /* Send Authorization and/or Upgrade request to server */
        prot_puts(s->out, "OPTIONS * HTTP/1.1\r\n");
        prot_printf(s->out, "Host: %s\r\n", s->hostname);
        prot_printf(s->out, "User-Agent: %s\r\n", buf_cstring(&serverinfo));
        if (scheme) {
            prot_printf(s->out, "Authorization: %s %s\r\n",
                        scheme->name, clientout ? clientout : "");
            prot_printf(s->out, "Authorize-As: %s\r\n",
                        userid ? userid : "anonymous");
        }
        else {
            prot_printf(s->out, "Upgrade: %s\r\n", TLS_VERSION);
            if (need_tls) {
                prot_puts(s->out, "Connection: Upgrade\r\n");
                need_tls = 0;
            }
            prot_puts(s->out, "Authorization: \r\n");
        }
        prot_puts(s->out, "\r\n");
        prot_flush(s->out);

        serverin = clientout = NULL;
        serverinlen = clientoutlen = 0;

        /* Read response(s) from backend until final response or error */
        do {
            resp_body.flags = BODY_DISCARD;
            r = http_read_response(s, METH_OPTIONS, &code,
                                   &hdrs, &resp_body, &errstr);
            if (r) {
                if (status) *status = errstr;
                break;
            }

            if (code == 101) {  /* Switching Protocols */
                if (tls_done) {
                    r = HTTP_BAD_GATEWAY;
                    if (status) *status = "TLS already active";
                    break;
                }
                else if (backend_starttls(s, NULL, NULL, NULL)) {
                    r = HTTP_SERVER_ERROR;
                    if (status) *status = "Unable to start TLS";
                    break;
                }
                else tls_done = 1;
            }
        } while (code < 200);

        switch (code) {
        default: /* Failure */
            if (!r) {
                r = HTTP_BAD_GATEWAY;
                if (status) {
                    buf_reset(&buf);
                    buf_printf(&buf,
                               "Unexpected status code from backend: %u", code);
                    *status = buf_cstring(&buf);
                }
            }
            break;

        case 426: /* Upgrade Required */
            if (tls_done) {
                r = HTTP_BAD_GATEWAY;
                if (status) *status = "TLS already active";
            }
            else need_tls = 1;
            break;

        case 200: /* OK */
            if (scheme->recv_success &&
                (serverin = scheme->recv_success(hdrs))) {
                /* Process success data */
                serverinlen = strlen(serverin);
                goto challenge;
            }
            break;

        case 401: /* Unauthorized */
            if (auth_done) {
                r = SASL_BADAUTH;
                break;
            }

            if (!serverin) {
                int i = 0;

                hdr = spool_getheader(hdrs, "WWW-Authenticate");

                if (!scheme) {
                    unsigned avail_auth_schemes = 0;
                    const char *mech = NULL;
                    size_t len;

                    /* Compare authentication schemes offered in
                     * WWW-Authenticate header(s) to what we support */
                    buf_reset(&buf);
                    for (i = 0; hdr && hdr[i]; i++) {
                        len = strcspn(hdr[i], " ");

                        for (scheme = auth_schemes; scheme->name; scheme++) {
                            if (!strncmp(scheme->name, hdr[i], len) &&
                                !((scheme->flags & AUTH_NEED_PERSIST) &&
                                  (resp_body.flags & BODY_CLOSE))) {
                                /* Tag the scheme as available */
                                avail_auth_schemes |= (1 << scheme->idx);

                                /* Add SASL-based schemes to SASL mech list */
                                if (scheme->saslmech) {
                                    if (buf_len(&buf)) buf_putc(&buf, ' ');
                                    buf_appendcstr(&buf, scheme->saslmech);
                                }
                                break;
                            }
                        }
                    }

                    /* If we have a mech_conf, use it */
                    if (mech_conf && buf_len(&buf)) {
                        char *conf = xstrdup(mech_conf);
                        char *newmechlist =
                            intersect_mechlists(conf,
                                                (char *) buf_cstring(&buf));

                        if (newmechlist) {
                            buf_setcstr(&buf, newmechlist);
                            free(newmechlist);
                        }
                        else {
                            syslog(LOG_DEBUG, "%s did not offer %s",
                                   s->hostname, mech_conf);
                            buf_reset(&buf);
                        }
                        free(conf);
                    }

#ifdef SASL_HTTP_REQUEST
                    /* Set HTTP request as specified above (REQUIRED) */
                    httpreq.non_persist = (resp_body.flags & BODY_CLOSE);
                    sasl_setprop(s->saslconn, SASL_HTTP_REQUEST, &httpreq);
#endif

                    /* Try to start SASL exchange using available mechs */
                    r = sasl_client_start(s->saslconn, buf_cstring(&buf),
                                          NULL,         /* no prompts */
                                          NULL, NULL,   /* no initial resp */
                                          &mech);

                    if (mech) {
                        /* Find auth scheme associated with chosen SASL mech */
                        for (scheme = auth_schemes; scheme->name; scheme++) {
                            if (scheme->saslmech &&
                                !strcmp(scheme->saslmech, mech)) break;
                        }
                    }
                    else {
                        /* No matching SASL mechs - try Basic */
                        scheme = &auth_schemes[AUTH_BASIC];
                        if (!(avail_auth_schemes & (1 << scheme->idx))) {
                            need_tls = !tls_done;
                            break;  /* case 401 */
                        }
                    }

                    /* Find the associated WWW-Authenticate header */
                    for (i = 0; hdr && hdr[i]; i++) {
                        len = strcspn(hdr[i], " ");
                        if (!strncmp(scheme->name, hdr[i], len)) break;
                    }
                }

                /* Get server challenge, if any */
                if (hdr) {
                    const char *p = strchr(hdr[i], ' ');
                    serverin = p ? ++p : "";
                    serverinlen = strlen(serverin);
                }
            }

        challenge:
            if (serverin) {
                /* Perform the next step in the auth exchange */

                if (scheme->idx == AUTH_BASIC) {
                    /* Don't care about "realm" in server challenge */
                    const char *authid =
                        callback_getdata(s->saslconn, cb, SASL_CB_AUTHNAME);
                    pass = callback_getdata(s->saslconn, cb, SASL_CB_PASS);

                    buf_reset(&buf);
                    buf_printf(&buf, "%s:%s", authid, pass);
                    clientout = buf_cstring(&buf);
                    clientoutlen = buf_len(&buf);
                    auth_done = 1;
                }
                else {
                    /* Base64 decode any server challenge, if necessary */
                    if (serverin && (scheme->flags & AUTH_BASE64)) {
                        r = sasl_decode64(serverin, serverinlen,
                                          base64, BASE64_BUF_SIZE, &serverinlen);
                        if (r != SASL_OK) break;  /* case 401 */

                        serverin = base64;
                    }

                    /* SASL mech (Digest, Negotiate, NTLM) */
                    r = sasl_client_step(s->saslconn, serverin, serverinlen,
                                         NULL,          /* no prompts */
                                         &clientout, &clientoutlen);
                    if (r == SASL_OK) auth_done = 1;
                }
            }
            break;  /* case 401 */
        }

    } while (need_tls || clientout);

  done:
    if (hdrs) spool_free_hdrcache(hdrs);

    if (r && status && !*status) *status = sasl_errstring(r, NULL, NULL);

    return r;
}


static int ping(struct backend *s, const char *userid)
{
    unsigned code = 0;
    const char *errstr;
    hdrcache_t resp_hdrs = NULL;
    struct body_t resp_body;

    /* Send Authorization request to server */
    prot_puts(s->out, "OPTIONS * HTTP/1.1\r\n");
    prot_printf(s->out, "Host: %s\r\n", s->hostname);
    prot_printf(s->out, "User-Agent: %s\r\n", buf_cstring(&serverinfo));
    prot_printf(s->out, "Authorize-As: %s\r\n", userid ? userid : "anonymous");
    prot_puts(s->out, "\r\n");
    prot_flush(s->out);

    /* Read response(s) from backend until final response or error */
    do {
        resp_body.flags = BODY_DISCARD;
        if (http_read_response(s, METH_OPTIONS, &code,
                               &resp_hdrs, &resp_body, &errstr)) {
            break;
        }
    } while (code < 200);

    if (resp_hdrs) spool_free_hdrcache(resp_hdrs);

    return (code != 200);
}


static int logout(struct backend *s __attribute__((unused)))
{
    /* Nothing to send, client just closes connection */
    return 0;
}


/* proxy mboxlist_lookup; on misses, it asks the listener for this
 * machine to make a roundtrip to the master mailbox server to make
 * sure it's up to date
 */
EXPORTED int http_mlookup(const char *name, mbentry_t **mbentryp, void *tid)
{
    mbentry_t *mbentry = NULL;
    int r;

    r = mboxlist_lookup(name, &mbentry, tid);
    if (r == IMAP_MAILBOX_NONEXISTENT && config_mupdate_server) {
        kick_mupdate();
        r = mboxlist_lookup(name, &mbentry, tid);
    }
    if (r) return r;
    if (mbentry->mbtype & MBTYPE_RESERVE) {
        r = IMAP_MAILBOX_RESERVED;
        goto done;
    }
    if (mbentry->mbtype & MBTYPE_MOVING) {
        r = IMAP_MAILBOX_MOVED;
        goto done;
    }
    if (mbentry->mbtype & MBTYPE_DELETED) {
        r = IMAP_MAILBOX_NONEXISTENT;
        goto done;
    }

done:
    if (!r && mbentryp) *mbentryp = mbentry;
    else mboxlist_entry_free(&mbentry);
    return r;
}


/* Fetch protocol and host used for request from headers */
EXPORTED void http_proto_host(hdrcache_t req_hdrs, const char **proto, const char **host)
{
    const char **fwd;

    if (config_mupdate_server && config_getstring(IMAPOPT_PROXYSERVERS) &&
        (fwd = spool_getheader(req_hdrs, "Forwarded"))) {
        /* Proxied request - parse last Forwarded header for proto and host */
        /* XXX  This is destructive of the header but we don't care
         * and more importantly, we need the tokens available after tok_fini()
         */
        tok_t tok;
        char *token;

        while (fwd[1]) ++fwd;  /* Skip to last Forwarded header */

        tok_initm(&tok, (char *) fwd[0], ";", 0);
        while ((token = tok_next(&tok))) {
            if (proto && !strncmp(token, "proto=", 6)) *proto = token+6;
            else if (host && !strncmp(token, "host=", 5)) *host = token+5;
        }
        tok_fini(&tok);
    }
    else {
        /* Use our protocol and host */
        if (proto) *proto = https ? "https" : "http";
        if (host) *host = *spool_getheader(req_hdrs, "Host");
    }
}

/* Construct and write Via header to protstream. */
static void write_forwarding_hdrs(struct transaction_t *txn, hdrcache_t hdrs,
                                  const char *version, const char *proto)
{
    const char **via = spool_getheader(hdrs, "Via");
    const char **fwd = spool_getheader(hdrs, "Forwarded");

    /* Add any existing Via headers */
    for (; via && *via; via++) simple_hdr(txn, "Via", *via);

    /* Create our own Via header */
    simple_hdr(txn, "Via", (config_serverinfo == IMAP_ENUM_SERVERINFO_ON) ?
               "%s %s (Cyrus/%s)" : "%s %s",
               version+5, config_servername,cyrus_version());

    /* Add any existing Forwarded headers */
    for (; fwd && *fwd; fwd++) simple_hdr(txn, "Forwarded", *fwd);

    /* Create our own Forwarded header */
    if (proto) {
        const char **host = spool_getheader(hdrs, "Host");
        size_t len;

        assert(!buf_len(&txn->buf));
        buf_printf(&txn->buf, "proto=%s", proto);
        if (host) buf_printf(&txn->buf, ";host=%s", *host);
        if (httpd_remoteip) {
            len = strcspn(httpd_remoteip, ";");
            buf_printf(&txn->buf, ";for=%.*s", (int)len, httpd_remoteip);
        }
        if (httpd_localip) {
            len = strcspn(httpd_localip, ";");
            buf_printf(&txn->buf, ";for=%.*s", (int)len, httpd_localip);
        }

        simple_hdr(txn, "Forwarded", buf_cstring(&txn->buf));
        buf_reset(&txn->buf);
    }
}


/* Write end-to-end header (ignoring hop-by-hop) from cache to protstream. */
static void write_cachehdr(const char *name, const char *contents, void *rock)
{
    struct transaction_t *txn = (struct transaction_t *) rock;
    const char **hdr, *hop_by_hop[] =
        { "authorization", "connection", "content-length", "expect", "forwarded",
          "host", "http2-settings", "keep-alive", "strict-transport-security",
          "te", "trailer", "transfer-encoding", "upgrade", "via", NULL };

    /* Ignore private headers in our cache */
    if (name[0] == ':') return;

    for (hdr = hop_by_hop; *hdr && strcmp(name, *hdr); hdr++);

    if (!*hdr) {
        if (!strcmp(name, "max-forwards")) {
            /* Decrement Max-Forwards before forwarding */
            unsigned long max = strtoul(contents, NULL, 10);

            simple_hdr(txn, "Max-Forwards", "%lu", max-1);
        }
        else {
            simple_hdr(txn, name, contents);
        }
    }
}


static long resp_code_to_http_err(unsigned code)
{
    int i, len, n_msgs = et_http_error_table.n_msgs;
    const char * const *msgs = et_http_error_table.msgs;
    char buf[100];

    len = snprintf(buf, sizeof(buf), "%u ", code);

    for (i = 0; i < n_msgs; i++) {
        if (!strncmp(msgs[i], buf, len)) return et_http_error_table.base + i;
    }

    return HTTP_SERVER_ERROR;
}


/* Send a cached response to the client */
static void send_response(struct transaction_t *txn, long code,
                          hdrcache_t hdrs, struct buf *body)
{
    unsigned long len;

    /* Stop method processing alarm */
    alarm(0);

    /*
     * - Use cached Status Line
     * - Add/append-to Via: header
     * - Add our own hop-by-hop headers
     * - Use all cached end-to-end headers
     */
    begin_resp_headers(txn, code);
    write_forwarding_hdrs(txn, hdrs, HTTP_VERSION, NULL);

    if (txn->flags.conn && txn->flags.ver != VER_2) {
        /* Construct Connection header - HTTP/1.x only */
        const char *conn_tokens[] =
            { "close", "Upgrade", "Keep-Alive", NULL };
        const char *upgrade_tokens[] =
            { TLS_VERSION,
#ifdef HAVE_NGHTTP2
              NGHTTP2_CLEARTEXT_PROTO_VERSION_ID,
#endif
              NULL };

        comma_list_hdr(txn, "Connection", conn_tokens, txn->flags.conn);

        if (txn->flags.upgrade) {
            comma_list_hdr(txn, "Upgrade", upgrade_tokens, txn->flags.upgrade);
        }

        if (txn->flags.conn & CONN_KEEPALIVE) {
            simple_hdr(txn, "Keep-Alive", "timeout=%d", httpd_timeout);
        }
    }

    if (httpd_tls_done) {
        simple_hdr(txn, "Strict-Transport-Security", "max-age=600");
    }

    spool_enum_hdrcache(hdrs, &write_cachehdr, txn);

    if (!body || !(len = buf_len(body))) {
        /* Empty body -- use  payload headers from response, if any */
        const char **hdr;

        if ((hdr = spool_getheader(hdrs, "Transfer-Encoding"))) {
            txn->flags.te = TE_CHUNKED;

            if (txn->flags.ver == VER_1_1) {
                simple_hdr(txn, "Transfer-Encoding", hdr[0]);
            }
            if ((hdr = spool_getheader(hdrs, "Trailer"))) {
                txn->flags.trailer = TRAILER_PROXY;
                simple_hdr(txn, "Trailer", hdr[0]);
            }
        }
        else if ((hdr = spool_getheader(hdrs, "Content-Length"))) {
            if (txn->flags.ver == VER_2) {
                /* Prevent end of stream */
                txn->flags.te = TE_CHUNKED;
            }
            else simple_hdr(txn, "Content-Length", hdr[0]);
        }

        end_resp_headers(txn, code);
    }
    else {
        /* Body is buffered, so send using "identity" TE */
        if (txn->flags.ver != VER_2)
            simple_hdr(txn, "Content-Length", "%lu", len);
        end_resp_headers(txn, code);
        write_body(0, txn, buf_base(body), len);
    }
}


/* Proxy (pipe) a chunk of body data to a client/server. */
static unsigned pipe_chunk(struct protstream *pin, struct transaction_t *txn,
                           unsigned len)
{
    char buf[PROT_BUFSIZE];
    unsigned n = 0;

    /* Read 'len' octets */
    for (; len; len -= n) {
        n = prot_read(pin, buf, MIN(len, PROT_BUFSIZE));
        if (!n) break;

        write_body(0, txn, buf, n);
    }

    return n;
}


/* Proxy (pipe) a response body to a client/server. */
static int pipe_resp_body(struct protstream *pin, struct transaction_t *txn,
                          hdrcache_t resp_hdrs, struct body_t *resp_body)
{
    char buf[PROT_BUFSIZE];
    const char **errstr = &txn->error.desc;

    txn->resp_body.enc = CE_IDENTITY;
    txn->flags.te = TE_NONE;

    if (resp_body->framing == FRAMING_UNKNOWN) {
        /* Get message framing */
        int r = http_parse_framing(0, resp_hdrs, resp_body, &txn->error.desc);
        if (r) return r;
    }

    /* Read and pipe the body */
    switch (resp_body->framing) {
    case FRAMING_LENGTH:
        /* Read 'len' octets */
        if (resp_body->len && !pipe_chunk(pin, txn, resp_body->len)) {
            syslog(LOG_ERR, "prot_read() error");
            *errstr = "Unable to read body data";
            return HTTP_BAD_GATEWAY;
        }
        break;

    case FRAMING_CHUNKED: {
        unsigned chunk;
        char *c;

        txn->flags.te = TE_CHUNKED;

        /* Read chunks until last-chunk (zero chunk-size) */
        do {
            /* Read chunk-size */
            prot_NONBLOCK(pin);
            c = prot_fgets(buf, PROT_BUFSIZE, pin);
            prot_BLOCK(pin);
            if (!c) c = prot_fgets(buf, PROT_BUFSIZE, pin);
            if (!c || sscanf(buf, "%x", &chunk) != 1) {
                *errstr = "Unable to read chunk size";
                return HTTP_BAD_GATEWAY;

                /* XXX  Do we need to parse chunk-ext? */
            }
            else if (chunk > resp_body->max - resp_body->len)
                return HTTP_PAYLOAD_TOO_LARGE;

            if (chunk) {
                /* Read 'chunk' octets */
                if (!pipe_chunk(pin, txn, chunk)) {
                    syslog(LOG_ERR, "prot_read() error");
                    *errstr = "Unable to read chunk data";
                    return HTTP_BAD_GATEWAY;
                }
            }

            else {
                /* Send terminating chunk */
                write_body(0, txn, NULL, 0);

                /* Read any trailing headers */
                if (txn->flags.trailer == TRAILER_PROXY) {
                    hdrcache_t trailers = NULL;
                    int r =
                        http_read_headers(pin, 0 /* read_sep */,
                                          &trailers, errstr);
                    if (r) {
                        if (trailers) spool_free_hdrcache(trailers);
                        return (r != HTTP_SERVER_ERROR ? HTTP_BAD_GATEWAY: r);
                    }
                    begin_resp_headers(txn, 0);
                    spool_enum_hdrcache(trailers, &write_cachehdr, txn);
                    end_resp_headers(txn, 0);
                    spool_free_hdrcache(trailers);
                }
            }

            /* Read CRLF terminating the chunk/trailer */
            if (!prot_fgets(buf, sizeof(buf), pin)) {
                *errstr = "Missing CRLF following chunk/trailer";
                return HTTP_BAD_GATEWAY;
            }

        } while (chunk);

        break;
    }

    case FRAMING_CLOSE:
        /* Read until EOF */
        if (pipe_chunk(pin, txn, UINT_MAX) || !pin->eof)
            return HTTP_BAD_GATEWAY;

        break;

    default:
        /* XXX  Should never get here */
        *errstr = "Unknown length of body data";
        return HTTP_BAD_GATEWAY;
    }

    return 0;
}



/* Proxy (pipe) a client-request/server-response to/from a backend. */
EXPORTED int http_pipe_req_resp(struct backend *be, struct transaction_t *txn)
{
    int r = 0, sent_body = 0;
    xmlChar *uri;
    unsigned code;
    long http_err;
    const char **hdr;
    hdrcache_t resp_hdrs = NULL;
    struct body_t resp_body;
    struct http_connection be_conn;
    struct transaction_t be_txn;

    memset(&be_conn, 0, sizeof(struct http_connection));
    be_conn.pin = be->in;
    be_conn.pout = be->out;

    memset(&be_txn, 0, sizeof(struct transaction_t));
    be_txn.flags.ver = VER_1_1;
    be_txn.conn = &be_conn;
    

    /*
     * Send client request to backend:
     *
     * - Piece the Request Line back together
     * - Add/append-to Via: header
     * - Add Expect:100-continue header (for synchonicity)
     * - Use all cached end-to-end headers from client
     * - Body will be sent using "chunked" TE, since we might not have it yet
     */
    uri = xmlURIEscapeStr(BAD_CAST txn->req_uri->path, BAD_CAST "/");
    prot_printf(be->out, "%s %s", txn->req_line.meth, uri);
    free(uri);
    if (URI_QUERY(txn->req_uri)) {
        prot_printf(be->out, "?%s", URI_QUERY(txn->req_uri));
    }
    prot_printf(be->out, " %s\r\n", HTTP_VERSION);
    prot_printf(be->out, "Host: %s\r\n", be->hostname);
    write_forwarding_hdrs(&be_txn, txn->req_hdrs, txn->req_line.ver,
                          https ? "https" : "http");
    spool_enum_hdrcache(txn->req_hdrs, &write_cachehdr, &be_txn);
    if ((hdr = spool_getheader(txn->req_hdrs, "TE"))) {
        for (; *hdr; hdr++) prot_printf(be->out, "TE: %s\r\n", *hdr);
    }
    if (http_methods[txn->meth].flags & METH_NOBODY)
        prot_puts(be->out, "Content-Length: 0\r\n");
    else if (spool_getheader(txn->req_hdrs, "Transfer-Encoding") ||
        spool_getheader(txn->req_hdrs, "Content-Length")) {
        prot_puts(be->out, "Expect: 100-continue\r\n");
        prot_puts(be->out, "Transfer-Encoding: chunked\r\n");
    }
    prot_puts(be->out, "\r\n");
    prot_flush(be->out);
    buf_free(&be_txn.buf);

    /* Read response(s) from backend until final response or error */
    memset(&resp_body, 0, sizeof(struct body_t));

    do {
        r = http_read_response(be, txn->meth, &code,
                               &resp_hdrs, NULL, &txn->error.desc);
        if (r) break;

        http_err = resp_code_to_http_err(code);

        if (code == 100) { /* Continue */
            if (!sent_body++) {
                unsigned len;

                /* Read body from client */
                r = http_read_body(httpd_in, httpd_out, txn->req_hdrs,
                                   &txn->req_body, &txn->error.desc);
                if (r) {
                    /* Couldn't get the body and can't finish request */
                    txn->flags.conn = CONN_CLOSE;
                    break;
                }

                /* Send single-chunk body to backend to complete the request */
                if ((len = buf_len(&txn->req_body.payload))) {
                    prot_printf(be->out, "%x\r\n", len);
                    prot_putbuf(be->out, &txn->req_body.payload);
                    prot_puts(be->out, "\r\n");
                }
                prot_puts(be->out, "0\r\n\r\n");
                prot_flush(be->out);
            }
            else {
                begin_resp_headers(txn, http_err);
                spool_enum_hdrcache(resp_hdrs, &write_cachehdr, txn);
                end_resp_headers(txn, http_err);
            }
        }
    } while (code < 200);

    if (r) proxy_downserver(be);
    else if (code == 401) {
        /* Don't pipe a 401 response (discard body).
           Frontend should send its own 401 since it will process auth */
        resp_body.flags |= BODY_DISCARD;
        http_read_body(be->in, httpd_out,
                       resp_hdrs, &resp_body, &txn->error.desc);

        r = HTTP_UNAUTHORIZED;
    }
    else {
        /* Send response to client */
        send_response(txn, http_err, resp_hdrs, NULL);

        /* Not expecting a body for 204/304 response or any HEAD response */
        switch (code) {
        case 204: /* No Content */
        case 304: /* Not Modified */
            break;

        default:
            if (txn->meth == METH_HEAD) break;

            if (pipe_resp_body(be->in, txn, resp_hdrs, &resp_body)) {
                /* Couldn't pipe the body and can't finish response */
                txn->flags.conn = CONN_CLOSE;
            }
        }
    }

    if (resp_body.flags & BODY_CLOSE) proxy_downserver(be);

    if (resp_hdrs) spool_free_hdrcache(resp_hdrs);

    return r;
}


/*
 * Proxy a COPY/MOVE client-request when the source and destination are
 * on different backends.  This is handled as a GET from the source and
 * PUT on the destination, while obeying any Overwrite header.
 *
 * For a MOVE request, we also LOCK, DELETE, and possibly UNLOCK the source.
 *
 * XXX  This function buffers the response bodies of the LOCK & GET requests.
 *      The response body of the PUT request is piped to the client.
 */
EXPORTED int http_proxy_copy(struct backend *src_be, struct backend *dest_be,
                    struct transaction_t *txn)
{
    int r = 0, sent_body;
    unsigned code;
    long http_err;
    char *lock = NULL;
    const char **hdr;
    hdrcache_t resp_hdrs = NULL;
    struct body_t resp_body;

#define write_hdr(pout, name, hdrs)                                     \
    if ((hdr = spool_getheader(hdrs, name)))                            \
        for (; *hdr; hdr++) prot_printf(pout, "%s: %s\r\n", name, *hdr)


    resp_body.payload = txn->resp_body.payload;

    if (txn->meth == METH_MOVE) {
        /*
         * Send a LOCK request to source backend:
         *
         * - Use any relevant conditional headers specified by client
         */
        prot_printf(src_be->out, "LOCK %s %s\r\n"
                                 "Host: %s\r\n"
                                 "User-Agent: %s\r\n",
                    txn->req_tgt.path, HTTP_VERSION,
                    src_be->hostname, buf_cstring(&serverinfo));
        write_hdr(src_be->out, "If", txn->req_hdrs);
        write_hdr(src_be->out, "If-Match", txn->req_hdrs);
        write_hdr(src_be->out, "If-Unmodified-Since", txn->req_hdrs);
        write_hdr(src_be->out, "If-Schedule-Tag-Match", txn->req_hdrs);

        assert(!buf_len(&txn->buf));
        buf_printf_markup(&txn->buf, 0,
                          "<?xml version=\"1.0\" encoding=\"utf-8\" ?>");
        buf_printf_markup(&txn->buf, 0, "<D:lockinfo xmlns:D='DAV:'>");
        buf_printf_markup(&txn->buf, 1,
                          "<D:lockscope><D:exclusive/></D:lockscope>");
        buf_printf_markup(&txn->buf, 1,
                          "<D:locktype><D:write/></D:locktype>");
        buf_printf_markup(&txn->buf, 1, "<D:owner>%s</D:owner>", httpd_userid);
        buf_printf_markup(&txn->buf, 0, "</D:lockinfo>");

        prot_printf(src_be->out,
                    "Content-Type: application/xml; charset=utf-8\r\n"
                    "Content-Length: %u\r\n\r\n%s",
                    (unsigned)buf_len(&txn->buf), buf_cstring(&txn->buf));
        buf_reset(&txn->buf);

        prot_flush(src_be->out);

        /* Read response(s) from source backend until final response or error */
        resp_body.flags = 0;

        do {
            r = http_read_response(src_be, METH_LOCK, &code,
                                   &resp_hdrs, &resp_body, &txn->error.desc);
            if (r) {
                proxy_downserver(src_be);
                goto done;
            }
        } while (code < 200);

        /* Get lock token */
        if ((hdr = spool_getheader(resp_hdrs, "Lock-Token")))
            lock = xstrdup(*hdr);

        switch (code) {
        case 200:
            /* Success, continue */
            break;

        case 201:
            /* Created empty resource, treat as 404 (Not Found) */
            r = HTTP_NOT_FOUND;
            goto delete;

        case 409:
            /* Failed to create resource, treat as 404 (Not Found) */
            r = HTTP_NOT_FOUND;
            goto done;

        default:
            /* Send failure response to client */
            http_err = resp_code_to_http_err(code);
            send_response(txn, http_err, resp_hdrs, &resp_body.payload);
            goto done;
        }
    }


    /*
     * Send a GET request to source backend to fetch body:
     *
     * - Use any relevant conditional headers specified by client
     *   (if not already sent in LOCK request)
     */
    prot_printf(src_be->out, "GET %s %s\r\n"
                             "Host: %s\r\n"
                             "User-Agent: %s\r\n",
                txn->req_tgt.path, HTTP_VERSION,
                src_be->hostname, buf_cstring(&serverinfo));
    if (txn->meth != METH_MOVE) {
        write_hdr(src_be->out, "If", txn->req_hdrs);
        write_hdr(src_be->out, "If-Match", txn->req_hdrs);
        write_hdr(src_be->out, "If-Unmodified-Since", txn->req_hdrs);
        write_hdr(src_be->out, "If-Schedule-Tag-Match", txn->req_hdrs);
    }
    prot_puts(src_be->out, "\r\n");
    prot_flush(src_be->out);

    /* Read response(s) from source backend until final response or error */
    resp_body.flags = 0;

    do {
        r = http_read_response(src_be, METH_GET, &code,
                               &resp_hdrs, &resp_body, &txn->error.desc);
        if (r || (resp_body.flags & BODY_CLOSE)) {
            proxy_downserver(src_be);
            goto done;
        }
    } while (code < 200);

    if (code != 200) {
        /* Send failure response to client */
        http_err = resp_code_to_http_err(code);
        send_response(txn, http_err, resp_hdrs, &resp_body.payload);
        goto done;
    }


    /*
     * Send a synchonizing PUT request to dest backend:
     *
     * - Add Expect:100-continue header (for synchonicity)
     * - Obey Overwrite by adding If-None-Match header
     * - Use any TE, Prefer, Accept* headers specified by client
     * - Use Content-Type, -Encoding, -Language headers from GET response
     * - Body is buffered, so send using "identity" TE
     */
    prot_printf(dest_be->out, "PUT %s %s\r\n"
                              "Host: %s\r\n"
                              "User-Agent: %s\r\n"
                              "Expect: 100-continue\r\n",
                *spool_getheader(txn->req_hdrs, "Destination"), HTTP_VERSION,
                dest_be->hostname, buf_cstring(&serverinfo));
    hdr = spool_getheader(txn->req_hdrs, "Overwrite");
    if (hdr && !strcmp(*hdr, "F"))
        prot_puts(dest_be->out, "If-None-Match: *\r\n");
    write_hdr(dest_be->out, "TE", txn->req_hdrs);
    write_hdr(dest_be->out, "Prefer", txn->req_hdrs);
    write_hdr(dest_be->out, "Accept", txn->req_hdrs);
    write_hdr(dest_be->out, "Accept-Charset", txn->req_hdrs);
    write_hdr(dest_be->out, "Accept-Encoding", txn->req_hdrs);
    write_hdr(dest_be->out, "Accept-Language", txn->req_hdrs);
    write_hdr(dest_be->out, "Content-Type", resp_hdrs);
    write_hdr(dest_be->out, "Content-Encoding", resp_hdrs);
    write_hdr(dest_be->out, "Content-Language", resp_hdrs);
    prot_printf(dest_be->out, "Content-Length: %u\r\n\r\n",
                (unsigned)buf_len(&resp_body.payload));
    prot_flush(dest_be->out);

    /* Read response(s) from dest backend until final response or error */
    sent_body = 0;

    do {
        r = http_read_response(dest_be, METH_PUT, &code,
                               &resp_hdrs, NULL, &txn->error.desc);
        if (r) {
            proxy_downserver(dest_be);
            goto done;
        }

        if ((code == 100) /* Continue */  && !sent_body++) {
            /* Send body to dest backend to complete the PUT */
            prot_putbuf(dest_be->out, &resp_body.payload);
            prot_flush(dest_be->out);
        }
    } while (code < 200);

    /* Send response to client */
    http_err = resp_code_to_http_err(code);
    send_response(txn, http_err, resp_hdrs, NULL);
    if (code != 204) {
        resp_body.framing = FRAMING_UNKNOWN;
        if (pipe_resp_body(dest_be->in, txn, resp_hdrs, &resp_body)) {
            /* Couldn't pipe the body and can't finish response */
            txn->flags.conn = CONN_CLOSE;
            proxy_downserver(dest_be);
            goto done;
        }
    }


  delete:
    if ((txn->meth == METH_MOVE) && (code < 300)) {
        /*
         * Send a DELETE request to source backend:
         *
         * - Add If header with lock token
         */
        prot_printf(src_be->out, "DELETE %s %s\r\n"
                                 "Host: %s\r\n"
                                 "User-Agent: %s\r\n",
                    txn->req_tgt.path, HTTP_VERSION,
                    src_be->hostname, buf_cstring(&serverinfo));
        if (lock) prot_printf(src_be->out, "If: (%s)\r\n", lock);
        prot_puts(src_be->out, "\r\n");
        prot_flush(src_be->out);

        /* Read response(s) from source backend until final resp or error */
        resp_body.flags = BODY_DISCARD;

        do {
            if (http_read_response(src_be, METH_DELETE, &code,
                                   &resp_hdrs, &resp_body, &txn->error.desc)
                || (resp_body.flags & BODY_CLOSE)) {
                proxy_downserver(src_be);
                break;
            }
        } while (code < 200);

        if (code < 300 && lock) {
            free(lock);
            lock = NULL;
        }
    }


  done:
    if (lock) {
        /*
         * Something failed - Send an UNLOCK request to source backend:
         */
        prot_printf(src_be->out, "UNLOCK %s %s\r\n"
                                 "Host: %s\r\n"
                                 "User-Agent: %s\r\n"
                                 "Lock-Token: %s\r\n\r\n",
                    txn->req_tgt.path, HTTP_VERSION,
                    src_be->hostname, buf_cstring(&serverinfo), lock);
        prot_flush(src_be->out);

        /* Read response(s) from source backend until final resp or error */
        resp_body.flags = BODY_DISCARD;

        do {
            if (http_read_response(src_be, METH_UNLOCK, &code,
                                   &resp_hdrs, &resp_body, &txn->error.desc)) {
                proxy_downserver(src_be);
                break;
            }
        } while (code < 200);

        free(lock);
    }

    txn->resp_body.payload = resp_body.payload;
    if (resp_hdrs) spool_free_hdrcache(resp_hdrs);

    return r;
}
