feat(d5-daemon-motd): daemon MOTD display + --no-motd

src/shared/motd.c

@@ -0,0 +1,76 @@
+#include "motd.h"
+#include "protocol.h"
+#include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+char* motd_read_file(const char* path) {
+  if (!path || path[0] == '\0')
+    return NULL;
+  FILE* fp = fopen(path, "rb");
+  if (!fp)
+    return NULL;
+  char* buffer = malloc(MOTD_MAX_BYTES + 1);
+  if (!buffer) {
+    fclose(fp);
+    return NULL;
+  }
+  /* fread stops at the bound; a larger file is truncated rather than read
+   * unbounded.  ferror distinguishes a truncated read from an I/O failure. */
+  size_t total = fread(buffer, 1, MOTD_MAX_BYTES, fp);
+  if (ferror(fp)) {
+    free(buffer);
+    fclose(fp);
+    return NULL;
+  }
+  fclose(fp);
+  buffer[total] = '\0';
+  return buffer;
+}
+
+char* motd_render(const char* motd, bool eight_bit_output) {
+  if (!motd)
+    return NULL;
+  size_t length = strlen(motd);
+  if (length > (SIZE_MAX - 1) / 5)
+    return NULL;
+  char* rendered = malloc(length * 5 + 1);
+  if (!rendered)
+    return NULL;
+  size_t out = 0;
+  for (size_t i = 0; i < length; i++) {
+    unsigned char byte = (unsigned char)motd[i];
+    if (byte == '\n' || byte == '\t') {
+      rendered[out++] = (char)byte;
+    } else if ((byte >= 32 && byte <= 126) || (eight_bit_output && byte >= 128)) {
+      rendered[out++] = (char)byte;
+    } else {
+      rendered[out++] = '\\';
+      rendered[out++] = '#';
+      rendered[out++] = (char)('0' + ((byte >> 6) & 7));
+      rendered[out++] = (char)('0' + ((byte >> 3) & 7));
+      rendered[out++] = (char)('0' + (byte & 7));
+    }
+  }
+  rendered[out] = '\0';
+  return rendered;
+}
+
+bool motd_send(int file_descriptor, const char* motd) {
+  return send_str(file_descriptor, motd ? motd : "");
+}
+
+char* motd_receive(int file_descriptor) {
+  char* motd = receive_str(file_descriptor);
+  if (!motd)
+    return NULL;
+  /* Guard against a hostile/oversized peer: receive_str already bounded the
+   * frame at MAX_STRING_SIZE and consumed it, so discarding an over-bound
+   * body here keeps the stream framed while refusing to display it. */
+  if (strlen(motd) > MOTD_MAX_BYTES) {
+    free(motd);
+    return NULL;
+  }
+  return motd;
+}