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From: Junio C Hamano <gitster@pobox.com>
To: Patrick Steinhardt <ps@pks.im>
Cc: git <git@vger.kernel.org>, Christian Couder <christian.couder@gmail.com>
Subject: Re: [PATCH 3/9] strbuf: provide function to append whole lines
Date: Fri, 27 Mar 2020 14:04:18 -0700
Message-ID: <xmqqpncxfr1p.fsf@gitster.c.googlers.com> (raw)
In-Reply-To: <4b0a963ea5c47a951b95aa0a03966315b3e8299d.1585129842.git.ps@pks.im> (Patrick Steinhardt's message of "Wed, 25 Mar 2020 10:53:47 +0100")

Patrick Steinhardt <ps@pks.im> writes:

> While the strbuf interface already provides functions to read a line
> into it that completely replaces its current contents, we do not have an
> interface that allows for appending lines without discarding current
> contents.
>
> Add a new function `strbuf_appendwholeline` that reads a line including
> its terminating character into a strbuf non-destructively. This is a
> preparatory step for git-update-ref(1) reading standard input line-wise
> instead of as a block.

Hmph.  If we were to gain more uses of this function over time, the
necessity for an extra strbuf_addbuf() becomes annoying.  I wonder
if we should be doing this patch the other way around, i.e. move the
whole implementation, except for the early

	if (feof(fp))
		return EOF;
	strbuf_reset(sb);

part, and call it strbuf_addwholeline(), and strbuf_getwholeline()
becomes a thin wrapper around it that resets the incoming buffer
before calling strbuf_addwholeline().  The logic to determine EOF
would need to be updated if we go that route (i.e. instead of
checking sb->len is zero in the !HAVE_GETDELIM side of the
implementation, we need to see if the number is the same as before)
but it should be minor.

There is a stale comment in the HAVE_GETDELIM side of the curent
implementation, by the way.  I think our xrealloc no longer tries
to "recover" from ENOMEM.

Having said all that, I am fine with this version, at least for now.

> +int strbuf_appendwholeline(struct strbuf *sb, FILE *fp, int term)
> +{
> +	struct strbuf line = STRBUF_INIT;
> +	if (strbuf_getwholeline(&line, fp, term))
> +		return EOF;

So, if caller wants to read the stream until it runs out, it can do

	strbuf_init(&sb);
	while (strbuf_appendwholeline(&sb, fp, '\n') != EOF)
		; /* keep going */

If the caller knows how many lines to read, EOF-return can be used
only for error checking, e.g.

	strbuf_init(&sb);
	for (count = 0; count < 5; count++)
		if (strbuf_appendwholeline(&sb, fp, '\n') == EOF)
			die("cannot grab 5 lines");

It becomes cumbersome if the input lines are terminated, though.
The caller wouldn't be using strbuf_appendwholeline() interface,
e.g.

	strbuf_init(&accum);
	while ((strbuf_getwholeline(&sb, fp, '\n') != EOF) &&
               strcmp(sb.buf, "done\n"))
		strbuf_addbuf(&accum, &sb);

Anyway, I was primarily wondering if returning EOF, which perfectly
makes sense for getwholeline(), still makes sense for addwholeline(),
and it seems that it is still useful.

> +	strbuf_addbuf(sb, &line);
> +	strbuf_release(&line);
> +	return 0;
> +}
> +
>  static int strbuf_getdelim(struct strbuf *sb, FILE *fp, int term)
>  {
>  	if (strbuf_getwholeline(sb, fp, term))
> diff --git a/strbuf.h b/strbuf.h
> index ce8e49c0b2..411063ca76 100644
> --- a/strbuf.h
> +++ b/strbuf.h
> @@ -502,6 +502,12 @@ int strbuf_getline(struct strbuf *sb, FILE *file);
>   */
>  int strbuf_getwholeline(struct strbuf *sb, FILE *file, int term);
>  
> +/**
> + * Like `strbuf_getwholeline`, but appends the line instead of
> + * resetting the buffer first.
> + */
> +int strbuf_appendwholeline(struct strbuf *sb, FILE *file, int term);
> +
>  /**
>   * Like `strbuf_getwholeline`, but operates on a file descriptor.
>   * It reads one character at a time, so it is very slow.  Do not

  reply index

Thread overview: 48+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-03-25  9:53 [PATCH 0/9] Support for transactions in `git-update-ref --stdin` Patrick Steinhardt
2020-03-25  9:53 ` [PATCH 1/9] refs: fix segfault when aborting empty transaction Patrick Steinhardt
2020-03-27 19:59   ` Junio C Hamano
2020-03-25  9:53 ` [PATCH 2/9] git-update-ref.txt: add missing word Patrick Steinhardt
2020-03-25  9:53 ` [PATCH 3/9] strbuf: provide function to append whole lines Patrick Steinhardt
2020-03-27 21:04   ` Junio C Hamano [this message]
2020-03-30 13:25     ` Patrick Steinhardt
2020-03-30 17:12       ` Junio C Hamano
2020-03-25  9:53 ` [PATCH 4/9] update-ref: organize commands in an array Patrick Steinhardt
2020-03-27 21:25   ` Junio C Hamano
2020-03-30  8:05     ` Patrick Steinhardt
2020-03-30 16:55       ` Junio C Hamano
2020-03-30 17:37         ` Patrick Steinhardt
2020-03-25  9:54 ` [PATCH 5/9] update-ref: drop unused argument for `parse_refname` Patrick Steinhardt
2020-03-25  9:54 ` [PATCH 6/9] update-ref: pass end pointer instead of strbuf Patrick Steinhardt
2020-03-25  9:54 ` [PATCH 7/9] update-ref: move transaction handling into `update_refs_stdin()` Patrick Steinhardt
2020-03-27 21:44   ` Junio C Hamano
2020-03-25  9:54 ` [PATCH 8/9] update-ref: read commands in a line-wise fashion Patrick Steinhardt
2020-03-27 21:58   ` Junio C Hamano
2020-03-30  8:11     ` Patrick Steinhardt
2020-03-30 17:39       ` Junio C Hamano
2020-03-25  9:54 ` [PATCH 9/9] update-ref: implement interactive transaction handling Patrick Steinhardt
2020-03-27 22:00   ` Junio C Hamano
2020-03-30 13:46 ` [PATCH v2 0/9] Support for transactions in `git-update-ref --stdin` Patrick Steinhardt
2020-03-30 13:46   ` [PATCH v2 1/9] refs: fix segfault when aborting empty transaction Patrick Steinhardt
2020-03-30 13:46   ` [PATCH v2 2/9] git-update-ref.txt: add missing word Patrick Steinhardt
2020-03-30 13:46   ` [PATCH v2 3/9] strbuf: provide function to append whole lines Patrick Steinhardt
2020-03-30 13:46   ` [PATCH v2 4/9] update-ref: organize commands in an array Patrick Steinhardt
2020-03-30 13:46   ` [PATCH v2 5/9] update-ref: drop unused argument for `parse_refname` Patrick Steinhardt
2020-03-30 13:46   ` [PATCH v2 6/9] update-ref: pass end pointer instead of strbuf Patrick Steinhardt
2020-03-30 13:46   ` [PATCH v2 7/9] update-ref: move transaction handling into `update_refs_stdin()` Patrick Steinhardt
2020-03-30 13:46   ` [PATCH v2 8/9] update-ref: read commands in a line-wise fashion Patrick Steinhardt
2020-03-30 13:47   ` [PATCH v2 9/9] update-ref: implement interactive transaction handling Patrick Steinhardt
2020-04-02  7:09 ` [PATCH v3 0/9] Support for transactions in `git-update-ref --stdin` Patrick Steinhardt
2020-04-02  7:09   ` [PATCH v3 1/9] refs: fix segfault when aborting empty transaction Patrick Steinhardt
2020-04-02  7:09   ` [PATCH v3 2/9] git-update-ref.txt: add missing word Patrick Steinhardt
2020-04-02  7:09   ` [PATCH v3 3/9] strbuf: provide function to append whole lines Patrick Steinhardt
2020-04-02  7:09   ` [PATCH v3 4/9] update-ref: organize commands in an array Patrick Steinhardt
2020-04-02  7:09   ` [PATCH v3 5/9] update-ref: drop unused argument for `parse_refname` Patrick Steinhardt
2020-04-02  7:09   ` [PATCH v3 6/9] update-ref: pass end pointer instead of strbuf Patrick Steinhardt
2020-04-02  7:09   ` [PATCH v3 7/9] update-ref: move transaction handling into `update_refs_stdin()` Patrick Steinhardt
2020-04-02  7:09   ` [PATCH v3 8/9] update-ref: read commands in a line-wise fashion Patrick Steinhardt
2020-04-02  7:10   ` [PATCH v3 9/9] update-ref: implement interactive transaction handling Patrick Steinhardt
2020-04-03 13:40     ` Phillip Wood
2020-04-03 16:51       ` Patrick Steinhardt
2020-04-03 17:33       ` Junio C Hamano
2020-04-03 17:35         ` Junio C Hamano
2020-04-06  7:10         ` Patrick Steinhardt

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