add support for the proxy protocol v1

This allows to use proxies like nginx or haproxy in front of gmid and
still have the correct information about the originating client.

This will need explicit opt-in via the `proxy-v1' listen flag which
will be added in a follow-up commit.

Merges https://github.com/omar-polo/gmid/pull/30

1 files changed, 213 insertions, 0 deletions

diff --git a/proxy-proto.c b/proxy-proto.c
new file mode 100644
index 0000000..e90c851
--- /dev/null
+++ b/proxy-proto.c
@@ -0,0 +1,213 @@
+/*
+ * Copyright (c) 2024 github.com/Sir-Photch <sir-photch@posteo.me>
+ *
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, 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 "gmid.h"
+
+#include <stdint.h>
+#include <string.h>
+
+#define MIN(a, b) (a) < (b) ? (a) : (b)
+
+static int 
+check_prefix_v1(char **buf)
+{
+    static const char PROXY[6] = "PROXY ";
+
+    if (0 != strncmp(*buf, PROXY, sizeof(PROXY)))
+        return PROXY_PROTO_PARSE_FAIL;
+
+    *buf += sizeof(PROXY);
+
+    return PROXY_PROTO_PARSE_SUCCESS;
+}
+
+static int
+check_proto_v1(char **buf)
+{
+    static const char TCP[3] = "TCP";
+
+    if (0 != strncmp(*buf, TCP, sizeof(TCP)))
+        return PROXY_PROTO_PARSE_FAIL;
+
+    *buf += sizeof(TCP);
+
+    int type;
+    switch ((*buf)[0]) {
+        case '4': type = 4; break;
+        case '6': type = 6; break;
+        default: return PROXY_PROTO_PARSE_FAIL;
+    }
+
+    // '4' / '6' + ' '
+    *buf += 2;
+
+    return type;
+}
+
+static int
+check_unknown_v1(char **buf)
+{
+    static const char UNKNOWN[7] = "UNKNOWN";
+
+    if (0 != strncmp(*buf, UNKNOWN, sizeof(UNKNOWN)))
+        return PROXY_PROTO_PARSE_FAIL;
+
+    *buf += sizeof(UNKNOWN);
+
+    return PROXY_PROTO_PARSE_SUCCESS;
+}
+
+static int
+check_crlf_v1(char *const *buf, size_t buflen)
+{
+    static const char CRLF[2] = "\r\n";
+
+    if (buflen < sizeof(CRLF))
+        return PROXY_PROTO_PARSE_FAIL;
+
+    if (!memmem(*buf, buflen, CRLF, sizeof(CRLF)))
+        return PROXY_PROTO_PARSE_FAIL;
+
+    return PROXY_PROTO_PARSE_SUCCESS;
+}
+
+static int
+check_ip_v1(int af, void *addr, char **buf)
+{
+    char *spc;
+
+    if (NULL == (spc = strchr(*buf, ' ')))
+        return PROXY_PROTO_PARSE_FAIL;
+
+    *spc++ = '\0';
+
+    if (1 != inet_pton(af, *buf, addr))
+        return PROXY_PROTO_PARSE_FAIL;
+
+    *buf = spc;
+
+    return PROXY_PROTO_PARSE_SUCCESS;
+}
+
+static int
+check_port_v1(uint16_t *port, char **buf, size_t *buflen)
+{
+    size_t wspc_idx = strcspn(*buf, " \r");
+    char *wspc = *buf + wspc_idx;
+
+    if (!(' ' == *wspc || '\r' == *wspc))
+        return PROXY_PROTO_PARSE_FAIL;
+
+    *wspc++ = '\0';
+
+    const char *errstr;
+    long long num = strtonum(*buf, 0, UINT16_MAX, &errstr);
+    if (errstr)
+        return PROXY_PROTO_PARSE_FAIL;
+
+    *buf = wspc;
+    *port = num;
+
+    return PROXY_PROTO_PARSE_SUCCESS;
+}
+
+#define EXPECT_SUCCESS(call) do { \
+    ret = (call); \
+    if (PROXY_PROTO_PARSE_SUCCESS != ret) \
+        return ret; \
+} while (0)
+
+int proxy_proto_v1_parse(struct proxy_protocol_v1 *s, char *buf, size_t buflen, size_t *consumed)
+{
+    const char *begin = buf;
+    int ret;
+
+    EXPECT_SUCCESS(check_crlf_v1(&buf, buflen));
+    EXPECT_SUCCESS(check_prefix_v1(&buf));
+    
+    ret = check_proto_v1(&buf);
+    switch (ret) 
+    {
+        case 4: s->proto = PROTO_V4; break;
+        case 6: s->proto = PROTO_V6; break;
+        case PROXY_PROTO_PARSE_FAIL: {
+            EXPECT_SUCCESS(check_unknown_v1(&buf));
+
+            s->proto = PROTO_UNKNOWN;
+            return PROXY_PROTO_PARSE_SUCCESS;
+        } break;
+        default: return ret;
+    }
+
+    switch (s->proto)
+    {
+        case PROTO_V4: {
+            EXPECT_SUCCESS(check_ip_v1(AF_INET, &s->srcaddr.v4, &buf));
+            EXPECT_SUCCESS(check_ip_v1(AF_INET, &s->dstaddr.v4, &buf));
+        } break;
+
+        case PROTO_V6: {
+            EXPECT_SUCCESS(check_ip_v1(AF_INET6, &s->srcaddr.v6, &buf));
+            EXPECT_SUCCESS(check_ip_v1(AF_INET6, &s->dstaddr.v6, &buf));
+        } break;
+
+        default: ASSERT_MSG(0, "unimplemented");
+    }
+
+    EXPECT_SUCCESS(check_port_v1(&s->srcport, &buf, &buflen));
+    EXPECT_SUCCESS(check_port_v1(&s->dstport, &buf, &buflen));
+
+    assert('\n' == *buf);
+    buf += 1;
+
+    *consumed = buf - begin;
+    return PROXY_PROTO_PARSE_SUCCESS;
+}
+
+int 
+proxy_proto_v1_string(const struct proxy_protocol_v1 *s, char* buf, size_t buflen)
+{
+    // "0000:0000:0000:0000:0000:0000:0000:0000\0"
+    char srcaddrbuf[40], dstaddrbuf[40];
+    int ret;
+    switch (s->proto)
+    {
+        case PROTO_UNKNOWN: ret = snprintf(buf, buflen, "unknown"); goto fin;
+        case PROTO_V4: {
+            inet_ntop(AF_INET, &s->srcaddr.v4, srcaddrbuf, 39);
+            inet_ntop(AF_INET, &s->dstaddr.v4, dstaddrbuf, 39);
+        } break;
+        case PROTO_V6: {
+            inet_ntop(AF_INET6, &s->srcaddr.v6, srcaddrbuf, 39);
+            inet_ntop(AF_INET6, &s->dstaddr.v6, dstaddrbuf, 39);
+        } break;
+    }
+
+    srcaddrbuf[39] = dstaddrbuf[39] = '\0';
+
+    ret = snprintf(
+        buf,
+        buflen,
+        "from %s port %u via %s port %u",
+        srcaddrbuf,
+        s->srcport,
+        dstaddrbuf,
+        s->dstport
+    );
+
+fin:
+    return ret;
+}