docs: add docstrings to ~50 undocumented functions across C source files

common/config.py

@@ -1,3 +1,5 @@
+"""Deprecated config schema for the old fh_ob Python process. Kept so that
+common/log.py can be imported without errors. Not used at runtime."""
 import asyncio
 from pathlib import Path
 from typing import Optional

src/book.c

@@ -15,16 +15,19 @@
 static order_book_t g_books[MAX_SYMBOLS];
 static uint32_t g_book_count = 0;
 
+/* Zero out the global book array and reset count. */
 void book_init(void) {
     memset(g_books, 0, sizeof(g_books));
     g_book_count = 0;
 }
 
+/* Return book for a symbol index, or NULL if out of range. */
 order_book_t *book_get(uint16_t symbol_idx) {
     if (symbol_idx >= g_book_count) return NULL;
     return &g_books[symbol_idx];
 }
 
+/* Return the number of books currently stored. */
 uint32_t book_count(void) {
     return g_book_count;
 }

src/events.c

@@ -26,12 +26,15 @@
 #include <sys/socket.h>
 #include <arpa/inet.h>
 
+/* Set O_NONBLOCK on an fd. Returns 0 on success, -1 on error. */
 static int set_nonblocking(int fd) {
     int flags = fcntl(fd, F_GETFL, 0);
     if (flags < 0) return -1;
     return fcntl(fd, F_SETFL, flags | O_NONBLOCK);
 }
 
+/* Register an fd with the epoll set. If the fd is already tracked, modify
+   its events instead of re-adding. Returns 0 on success, -1 on error. */
 int event_loops_add_fd(epoll_set_t *set, int fd, fd_type_t type,
                        uint32_t ws_idx, void *user_data, uint32_t events) {
     if (set->fd_count >= MAX_EPOLL_FDS) {
@@ -63,6 +66,7 @@ int event_loops_add_fd(epoll_set_t *set, int fd, fd_type_t type,
     return epoll_ctl(set->epoll_fd, EPOLL_CTL_ADD, fd, &ev);
 }
 
+/* Remove an fd from the epoll set and mark its tracked entry as unused. */
 void event_loops_remove_fd(epoll_set_t *set, int fd) {
     epoll_ctl(set->epoll_fd, EPOLL_CTL_DEL, fd, NULL);
     for (uint32_t i = 0; i < set->fd_count; i++) {
@@ -73,6 +77,7 @@ void event_loops_remove_fd(epoll_set_t *set, int fd) {
     }
 }
 
+/* Initialise an epoll set: create epoll fd, zero the tracked fd array. */
 static void epoll_set_init(epoll_set_t *set) {
     memset(set, 0, sizeof(*set));
     set->epoll_fd = epoll_create1(EPOLL_CLOEXEC);
@@ -82,6 +87,8 @@ static void epoll_set_init(epoll_set_t *set) {
     }
 }
 
+/* Initialise both epoll sets (hot + cold), timer fd, and wakeup fd.
+   The cold epoll set monitors the wakeup eventfd for SPSC drain signals. */
 int event_loops_init(event_loops_t *loops, ws_client_t *ws_client,
                      spsc_queue_t *signal_queue, const config_t *cfg, int wakeup_fd) {
     memset(loops, 0, sizeof(*loops));
@@ -106,6 +113,7 @@ int event_loops_init(event_loops_t *loops, ws_client_t *ws_client,
     return 0;
 }
 
+/* Stop the event loops and close all fds (timer, eventfd, sockets, epolls). */
 void event_loops_destroy(event_loops_t *loops) {
     loops->running = false;
     if (loops->timer_fd >= 0) close(loops->timer_fd);
@@ -116,6 +124,9 @@ void event_loops_destroy(event_loops_t *loops) {
     if (loops->cold_epoll.epoll_fd >= 0) close(loops->cold_epoll.epoll_fd);
 }
 
+/* Connect to a Unix domain socket at the given path. Uses SOCK_NONBLOCK
+   with a poll-based 100ms timeout for the connection to complete.
+   Returns connected fd on success, -1 on failure. */
 int unix_client_connect(const char *socket_path) {
     int fd = socket(AF_UNIX, SOCK_STREAM | SOCK_NONBLOCK, 0);
     if (fd < 0) return -1;
@@ -139,6 +150,8 @@ int unix_client_connect(const char *socket_path) {
     return fd;
 }
 
+/* Create and bind a Unix domain stream socket server, remove stale socket
+   file first. Sets O_NONBLOCK on the listening fd. Returns fd, or -1. */
 int unix_server_create(const char *socket_path) {
     int fd = socket(AF_UNIX, SOCK_STREAM, 0);
     if (fd < 0) return -1;

src/hash.c

@@ -15,6 +15,7 @@
 static const uint32_t FNV_OFFSET = 2166136261u;
 static const uint32_t FNV_PRIME = 16777619u;
 
+/* FNV-1a non-cryptographic hash for arbitrary-length strings. */
 uint32_t fnv1a_hash(const char *str, uint32_t len) {
     uint32_t hash = FNV_OFFSET;
     for (uint32_t i = 0; i < len; i++) {
@@ -24,22 +25,27 @@ uint32_t fnv1a_hash(const char *str, uint32_t len) {
     return hash;
 }
 
+/* Initialise an empty symbol table with initial capacity. */
 void symbol_table_init(symbol_table_t *table) {
     table->capacity = SYMBOL_TABLE_INITIAL;
     table->count = 0;
     table->entries = calloc(table->capacity, sizeof(symbol_entry_t));
 }
 
+/* Compare two symbol entries by name (for bsearch). */
 static int entry_cmp(const void *a, const void *b) {
     const symbol_entry_t *ea = (const symbol_entry_t *)a;
     const symbol_entry_t *eb = (const symbol_entry_t *)b;
     return strcmp(ea->name, eb->name);
 }
 
+/* Wrapper matching qsort's comparison signature (same as entry_cmp). */
 static int entry_cmp_qsort(const void *a, const void *b) {
     return entry_cmp(a, b);
 }
 
+/* Sort entries by name and re-assign dense indices. Must be called after
+   all additions are complete, before any lookups via bsearch. */
 void symbol_table_sort(symbol_table_t *table) {
     qsort(table->entries, table->count, sizeof(symbol_entry_t), entry_cmp_qsort);
     for (uint32_t i = 0; i < table->count; i++) {
@@ -47,6 +53,8 @@ void symbol_table_sort(symbol_table_t *table) {
     }
 }
 
+/* Append a new symbol entry, doubling capacity if full. Returns the
+   assigned index, or -1 on allocation failure. */
 int symbol_table_add(symbol_table_t *table, const char *name) {
     if (table->count >= table->capacity) {
         uint32_t new_cap = table->capacity * 2;
@@ -66,6 +74,7 @@ int symbol_table_add(symbol_table_t *table, const char *name) {
     return (int)(table->count - 1);
 }
 
+/* Binary-search for a symbol by name. Returns its 16-bit index or -1. */
 int16_t symbol_table_lookup(const symbol_table_t *table, const char *name) {
     symbol_entry_t key;
     strncpy(key.name, name, SYMBOL_NAME_LEN - 1);

src/http_server.c

@@ -102,6 +102,7 @@ int http_server_accept(http_server_t *srv) {
     return srv->client_fd;
 }
 
+/* Write an HTTP response with status line, headers, and body to the client. */
 static void http_send(http_server_t *srv, const char *status,
                       const char *content_type, const char *body) {
     char header[512];
@@ -119,14 +120,17 @@ static void http_send(http_server_t *srv, const char *status,
     }
 }
 
+/* Send a 200 OK JSON response. */
 static void http_send_json(http_server_t *srv, const char *body) {
     http_send(srv, "200 OK", "application/json", body);
 }
 
+/* Send an error response with the given status code and plain text body. */
 static void http_send_error(http_server_t *srv, const char *status, const char *msg) {
     http_send(srv, status, "text/plain", msg);
 }
 
+/* GET /health — return WS connection count and symbol count as JSON. */
 static void handle_health(http_server_t *srv) {
     char body[256];
     int connected = 0;
@@ -141,6 +145,7 @@ static void handle_health(http_server_t *srv) {
     http_send_json(srv, body);
 }
 
+/* GET /book/{symbol} — return a single order book as JSON, or 404. */
 static void handle_book(http_server_t *srv, const char *symbol) {
     if (!srv->symbols || !srv->books) {
         http_send_error(srv, "500 Internal Server Error", "not initialized\n");
@@ -174,6 +179,7 @@ static void handle_book(http_server_t *srv, const char *symbol) {
     http_send_json(srv, body);
 }
 
+/* GET /books — return all order books as a JSON array. */
 static void handle_books(http_server_t *srv) {
     if (!srv->symbols || !srv->books) {
         http_send_error(srv, "500 Internal Server Error", "not initialized\n");
@@ -204,6 +210,7 @@ static void handle_books(http_server_t *srv) {
     http_send_json(srv, body);
 }
 
+/* GET /symbols — list all tracked symbol names as a JSON array. */
 static void handle_symbols_list(http_server_t *srv) {
     if (!srv->symbols) {
         http_send_error(srv, "500 Internal Server Error", "not initialized\n");
@@ -220,6 +227,7 @@ static void handle_symbols_list(http_server_t *srv) {
     http_send_json(srv, body);
 }
 
+/* POST /symbols — subscribe to new symbols (add to symbol table + WS subscribe). */
 static void handle_symbols_add(http_server_t *srv, const char *body) {
     if (!srv->symbols || !srv->ws_client) {
         http_send_error(srv, "500 Internal Server Error", "not initialized\n");
@@ -265,6 +273,7 @@ static void handle_symbols_add(http_server_t *srv, const char *body) {
     http_send_json(srv, resp);
 }
 
+/* DELETE /symbols/{name} — unsubscribe and remove from symbol table. */
 static void handle_symbols_remove(http_server_t *srv, const char *symbol) {
     if (!srv->symbols || !srv->ws_client) {
         http_send_error(srv, "500 Internal Server Error", "not initialized\n");

src/log.c

@@ -23,6 +23,8 @@ static int          log_pipe[2]  = {-1, -1};
 static pthread_t    log_thread;
 static atomic_bool  log_running = false;
 
+/* Background thread: drains the pipe and writes each chunk to stderr.
+   Spins on EAGAIN with 100us sleep when the pipe is empty. */
 static void *log_worker(void *arg) {
     (void)arg;
     char buf[4096];
@@ -43,6 +45,7 @@ static void *log_worker(void *arg) {
     return NULL;
 }
 
+/* Create a non-blocking pipe and start the background drain thread. */
 void log_init(void) {
     if (pipe2(log_pipe, O_NONBLOCK) != 0) {
         log_pipe[0] = log_pipe[1] = -1;
@@ -52,6 +55,7 @@ void log_init(void) {
     pthread_create(&log_thread, NULL, log_worker, NULL);
 }
 
+/* Stop the worker thread and close both pipe ends. */
 void log_shutdown(void) {
     atomic_store(&log_running, false);
     if (log_thread) {
@@ -61,6 +65,8 @@ void log_shutdown(void) {
     if (log_pipe[1] >= 0) { close(log_pipe[1]); log_pipe[1] = -1; }
 }
 
+/* Non-blocking log write. Formats a timestamped message into the pipe.
+   Falls back to sync stderr write if the pipe has not been initialised. */
 void log_write(const char *fmt, ...) {
     if (log_pipe[1] < 0) {
         /* fallback: sync write to stderr */

src/main.c

@@ -30,6 +30,8 @@
 
 static volatile sig_atomic_t g_running = 1;
 
+/* Set the global running flag to zero on SIGINT/SIGTERM. Thread-safe
+   via sig_atomic_t. The main loop checks g_running to exit cleanly. */
 static void signal_handler(int sig) {
     (void)sig;
     g_running = 0;

src/symbols_api.c

@@ -38,6 +38,7 @@ typedef struct {
     ph_entry_t entries[PAIR_HASH_SIZE];
 } pair_hash_t;
 
+/* Hash an unordered currency pair (a, b) to a bucket index (djb2 variant). */
 static uint32_t ph_hash(const char *a, const char *b) {
     uint32_t h = 5381;
     const uint8_t *s = (const uint8_t *)a;
@@ -47,10 +48,13 @@ static uint32_t ph_hash(const char *a, const char *b) {
     return h % PAIR_HASH_SIZE;
 }
 
+/* Zero-initialise the pair hash table. */
 static void ph_init(pair_hash_t *ph) {
     memset(ph, 0, sizeof(*ph));
 }
 
+/* Insert an unordered currency pair -> pair_index mapping with open
+   addressing linear probing. Silently ignores duplicates (keeps first). */
 static void ph_insert(pair_hash_t *ph, const char *c1, const char *c2, uint32_t idx) {
     // Normalize: store lexicographically smaller first for unordered lookup
     const char *a = c1, *b = c2;
@@ -67,6 +71,8 @@ static void ph_insert(pair_hash_t *ph, const char *c1, const char *c2, uint32_t
     ph->entries[h].used = true;
 }
 
+/* Look up an unordered currency pair, writing its index to *idx if found.
+   Returns true on hit, false on miss. */
 static bool ph_find(const pair_hash_t *ph, const char *c1, const char *c2, uint32_t *idx) {
     const char *a = c1, *b = c2;
     if (strcmp(a, b) > 0) { a = c2; b = c1; }

src/ws_client.c

@@ -45,6 +45,8 @@ static uint64_t now_realtime_ms(void) {
     return (uint64_t)ts.tv_sec * 1000 + ts.tv_nsec / 1000000;
 }
 
+/* Reset a WebSocket connection to its initial disconnected state, freeing
+   any SSL objects, BIOs, and the socket fd. Safe to call multiple times. */
 static void ws_connection_reset(ws_connection_t *conn) {
     conn->state = WS_STATE_DISCONNECTED;
     conn->read_pos = 0;
@@ -74,6 +76,7 @@ static void ws_connection_reset(ws_connection_t *conn) {
     }
 }
 
+/* Create a shared SSL context for all WS connections (TLS client, no peer verification). */
 static SSL_CTX *create_ssl_ctx(void) {
     SSL_CTX *ctx = SSL_CTX_new(TLS_client_method());
     if (!ctx) {
@@ -85,6 +88,8 @@ static SSL_CTX *create_ssl_ctx(void) {
     return ctx;
 }
 
+/* Resolve hostname via getaddrinfo and try each address until one connects.
+   Returns a connected socket fd, or -1 on failure. */
 static int resolve_and_connect(const char *host, int port) {
     struct addrinfo hints = {0}, *res = NULL;
     hints.ai_family = AF_UNSPEC;
@@ -112,6 +117,8 @@ static int resolve_and_connect(const char *host, int port) {
     return fd;
 }
 
+/* Create SSL object, set SNI hostname, attach socket fd, and perform TLS handshake.
+   Returns 0 on success, -1 on failure. */
 static int setup_tls(ws_connection_t *conn) {
     conn->ssl = SSL_new(conn->ctx);
     if (!conn->ssl) {
@@ -371,6 +378,9 @@ int ws_client_write(ws_connection_t *conn, const void *data, size_t len) {
  * Supports payload lengths < 126 (inline), < 65536 (16-bit ext), and >= 65536 (64-bit ext).
  * Masking key derived from monotonic clock to avoid predictable patterns.
  */
+/* Build and send an RFC 6455 WebSocket frame with masking.
+   Supports payload lengths < 126 (inline), < 65536 (16-bit ext), >= 65536 (64-bit ext).
+   Masking key derived from monotonic clock. Returns bytes sent on success, -1 on error. */
 static int ws_send_frame(ws_connection_t *conn, uint8_t opcode,
                          const uint8_t *payload, size_t payload_len) {
     uint8_t header[14];