change the encoder interface -- encoders always append the null byte,

except when the encoding is the empty string

src/base64.c

@@ -182,6 +182,7 @@ base64_encode(const enum encoding enc, char *restrict const buf,
 	}
 
 	assert(outlen > 0);
+	*p++ = '\0';
 	return p - buf;
 }
 

src/hex.c

@@ -134,6 +134,7 @@ hex_encode(const enum encoding enc, char *restrict const buf,
 		*p++ = alphabet[in[i] & 0x0f];
 	}
 
+	*p++ = '\0';
 	return p - buf;
 }
 

src/id.c

@@ -48,6 +48,7 @@ id_encode(const enum encoding enc, char *restrict const buf,
 		return 0;
 
 	memcpy(buf, in, inlen);
+	buf[inlen] = '\0';
 	return inlen;
 }
 

src/vmod_convert.h

@@ -60,8 +60,9 @@
  *
  * The regions pointed to by buf and in MUST NOT overlap (this is the
  * contract imposed by restrict).
- * An encoder SHALL NOT append the terminating null byte (this must
- * be done by the caller).
+ * An encoder SHALL append the terminating null byte if the length of
+ * the encoding is greater than 0; if the length is 0, the encoder
+ * SHALL NOT write the null byte.
  *
  * Returns:
  * -1, if there is insufficient space at buf, *including* space for the