Subject: [PATCH v3 0/3] pkt-line: war on magical `4` literal

From: Denton Liu <[email-masked]>
Date: Tue, 23 Jun 2020 13:55:31 -0400

There are many instances of the literal `4` in packet line-related code.
This series replaces these instances with either functions that can
generate the number or an appropriately-named constant.

Changes since v1:

* Introduce patch 1-2 so that the string length is used to generate the
  `4` where appropriate

Changes since v2:

* Replace some a couple of inline functions with macros that ensure they
  are string constants

* Use strlen() in one more instance over the PACKET_HEADER_SIZE

Denton Liu (3):
  remote-curl: use strlen() instead of magic numbers
  pkt-line: use string versions of functions
  pkt-line: extract out PACKET_HEADER_SIZE

 pkt-line.c    | 68 ++++++++++++++++++++++++++++++---------------------
 pkt-line.h    |  6 +++--
 remote-curl.c | 35 +++++++++++++-------------
 3 files changed, 62 insertions(+), 47 deletions(-)

Range-diff against v2:
1:  d2aaf15aa8 ! 1:  cb8683837c remote-curl: use strlen() instead of magic numbers
    @@ Metadata
      ## Commit message ##
         remote-curl: use strlen() instead of magic numbers
     
    -    When we are memcpy()ing the length header, we use the magic literal `4`,
    -    representing the length of "0000" and "0001", the packet line length
    -    headers. Use `strlen("000x")` so that we do not have to use the magic
    -    literal.
    +    When we are dealing with a packet-line length header, we use the magic
    +    literal `4`, representing the length of "0000" and "0001", the packet
    +    line length headers. Use `strlen("000x")` so that we do not have to use
    +    the magic literal.
     
      ## remote-curl.c ##
     @@ remote-curl.c: static int rpc_read_from_out(struct rpc_state *rpc, int options,
    @@ remote-curl.c: static int rpc_read_from_out(struct rpc_state *rpc, int options,
      			break;
      		case PACKET_READ_RESPONSE_END:
      			die(_("remote server sent stateless separator"));
    +@@ remote-curl.c: static int probe_rpc(struct rpc_state *rpc, struct slot_results *results)
    + 	curl_easy_setopt(slot->curl, CURLOPT_URL, rpc->service_url);
    + 	curl_easy_setopt(slot->curl, CURLOPT_ENCODING, NULL);
    + 	curl_easy_setopt(slot->curl, CURLOPT_POSTFIELDS, "0000");
    +-	curl_easy_setopt(slot->curl, CURLOPT_POSTFIELDSIZE, 4);
    ++	curl_easy_setopt(slot->curl, CURLOPT_POSTFIELDSIZE, strlen("0000"));
    + 	curl_easy_setopt(slot->curl, CURLOPT_HTTPHEADER, headers);
    + 	curl_easy_setopt(slot->curl, CURLOPT_WRITEFUNCTION, fwrite_buffer);
    + 	curl_easy_setopt(slot->curl, CURLOPT_FILE, &buf);
2:  8cab5078b1 ! 2:  d283a1b514 pkt-line: use string versions of functions
    @@ Commit message
         replaced with constants at compile-time so this should not result in any
         performance penalty.
     
    +
    + ## Notes ##
    +    Junio, you mentioned in an earlier email[0] that write_str_in_full() and
    +    strbuf_addstr() each count the string length at runtime. However, I
    +    don't think that's true since they're both inline functions and
    +    strbuf_addstr() has the following comment:
    +
    +    	/**
    +    	 * Add a NUL-terminated string to the buffer.
    +    	 *
    +    	 * NOTE: This function will *always* be implemented as an inline or a macro
    +    	 * using strlen, meaning that this is efficient to write things like:
    +    	 *
    +    	 *     strbuf_addstr(sb, "immediate string");
    +    	 *
    +    	 */
    +
    +    so I believe that the lengths should be determined at compile-time.
    +
    +    [0]: https://lore.kernel.org/git/[email-masked]/
    +
      ## pkt-line.c ##
     @@ pkt-line.c: static void packet_trace(const char *buf, unsigned int len, int write)
      	strbuf_release(&out);
    @@ pkt-line.c: static void packet_trace(const char *buf, unsigned int len, int writ
     +	packet_trace(buf, strlen(buf), write);
     +}
     +
    -+static inline void control_packet_write(int fd, const char *s, const char *type)
    -+{
    -+	packet_trace_str(s, 1);
    -+	if (write_str_in_full(fd, s) < 0)
    -+		die_errno(_("unable to write %s packet"), type);
    -+}
    ++#define control_packet_write(fd, s, errstr) \
    ++	do { \
    ++		(void)s"is a string constant"; \
    ++		packet_trace_str(s, 1); \
    ++		if (write_str_in_full((fd), s) < 0) \
    ++			die_errno((errstr)); \
    ++	} while (0)
     +
      /*
       * If we buffered things up above (we don't, but we should),
    @@ pkt-line.c: static void packet_trace(const char *buf, unsigned int len, int writ
     -	packet_trace("0000", 4, 1);
     -	if (write_in_full(fd, "0000", 4) < 0)
     -		die_errno(_("unable to write flush packet"));
    -+	control_packet_write(fd, "0000", "flush");
    ++	control_packet_write(fd, "0000", _("unable to write flush packet"));
      }
      
      void packet_delim(int fd)
    @@ pkt-line.c: static void packet_trace(const char *buf, unsigned int len, int writ
     -	packet_trace("0001", 4, 1);
     -	if (write_in_full(fd, "0001", 4) < 0)
     -		die_errno(_("unable to write delim packet"));
    -+	control_packet_write(fd, "0001", "delim");
    ++	control_packet_write(fd, "0001", _("unable to write delim packet"));
      }
      
      void packet_response_end(int fd)
    @@ pkt-line.c: static void packet_trace(const char *buf, unsigned int len, int writ
     -	packet_trace("0002", 4, 1);
     -	if (write_in_full(fd, "0002", 4) < 0)
     -		die_errno(_("unable to write stateless separator packet"));
    -+	control_packet_write(fd, "0002", "stateless separator");
    ++	control_packet_write(fd, "0002", _("unable to write stateless separator packet"));
      }
      
      int packet_flush_gently(int fd)
    @@ pkt-line.c: static void packet_trace(const char *buf, unsigned int len, int writ
      	return 0;
      }
      
    -+static inline void control_packet_buf_write(struct strbuf *buf, const char *s)
    -+{
    -+	packet_trace_str(s, 1);
    -+	strbuf_addstr(buf, s);
    -+}
    ++#define control_packet_buf_write(buf, s) \
    ++	do { \
    ++		(void)s"is a string constant"; \
    ++		packet_trace_str(s, 1); \
    ++		strbuf_addstr((buf), s); \
    ++	} while (0)
     +
      void packet_buf_flush(struct strbuf *buf)
      {
3:  585d8892c3 ! 3:  00c19983fd pkt-line: extract out PACKET_HEADER_SIZE
    @@ remote-curl.c: static void check_pktline(struct check_pktline_state *state, cons
      				}
      				state->len_filled = 0;
      			}
    -@@ remote-curl.c: static int probe_rpc(struct rpc_state *rpc, struct slot_results *results)
    - 	curl_easy_setopt(slot->curl, CURLOPT_URL, rpc->service_url);
    - 	curl_easy_setopt(slot->curl, CURLOPT_ENCODING, NULL);
    - 	curl_easy_setopt(slot->curl, CURLOPT_POSTFIELDS, "0000");
    --	curl_easy_setopt(slot->curl, CURLOPT_POSTFIELDSIZE, 4);
    -+	curl_easy_setopt(slot->curl, CURLOPT_POSTFIELDSIZE, PACKET_HEADER_SIZE);
    - 	curl_easy_setopt(slot->curl, CURLOPT_HTTPHEADER, headers);
    - 	curl_easy_setopt(slot->curl, CURLOPT_WRITEFUNCTION, fwrite_buffer);
    - 	curl_easy_setopt(slot->curl, CURLOPT_FILE, &buf);
     @@ remote-curl.c: int cmd_main(int argc, const char **argv)
      			parse_fetch(&buf);
      
-- 
2.27.0.307.g7979e895e7