qspawn: improve error reporting and handling

First off, avoid potential circular references (via {qx_arg}) by
dropping the {-qsp} field from $ctx and SolverGit objects.
Instead, we only share a reference to an optional error buffer
string {qsp_err}.

We'll also attempt to call qspawn.wcb if qx_cb fails, and warn
in more places w/o checking for $env since we now rely on warn()
instead of $env->{'psgi.errors'}.

This makes error handling simpler and safer in future callers.

3 files changed, 29 insertions, 33 deletions

diff --git a/lib/PublicInbox/Qspawn.pm b/lib/PublicInbox/Qspawn.pm
index 79db9e76..cea34fc3 100644
--- a/lib/PublicInbox/Qspawn.pm
+++ b/lib/PublicInbox/Qspawn.pm
@@ -1,4 +1,4 @@
-# Copyright (C) 2016-2021 all contributors <meta@public-inbox.org>
+# Copyright (C) all contributors <meta@public-inbox.org>
 # License: AGPL-3.0+ <https://www.gnu.org/licenses/agpl-3.0.txt>
 
 # Like most Perl modules in public-inbox, this is internal and
@@ -26,6 +26,7 @@
 
 package PublicInbox::Qspawn;
 use strict;
+use v5.10.1;
 use PublicInbox::Spawn qw(popen_rd);
 use PublicInbox::GzipFilter;
 
@@ -38,6 +39,7 @@ my $def_limiter;
 # $cmd is the command to spawn
 # $cmd_env is the environ for the child process (not PSGI env)
 # $opt can include redirects and perhaps other process spawning options
+# {qsp_err} is an optional error buffer callers may access themselves
 sub new ($$$;) {
         my ($class, $cmd, $cmd_env, $opt) = @_;
         bless { args => [ $cmd, $cmd_env, $opt ] }, $class;
@@ -93,18 +95,18 @@ sub finalize ($$) {
         }
 
         if ($err) {
-                if (defined $self->{err}) {
-                        $self->{err} .= "; $err";
-                } else {
-                        $self->{err} = $err;
-                }
-                if ($env && $self->{cmd}) {
-                        warn join(' ', @{$self->{cmd}}) . ": $err";
+                utf8::decode($err);
+                if (my $dst = $self->{qsp_err}) {
+                        $$dst .= $$dst ? " $err" : "; $err";
                 }
+                warn "@{$self->{cmd}}: $err" if $self->{cmd};
         }
         if ($qx_cb) {
                 eval { $qx_cb->($qx_buf, $qx_arg) };
-        } elsif (my $wcb = delete $env->{'qspawn.wcb'}) {
+                return unless $@;
+                warn "E: $@"; # hope qspawn.wcb can handle it
+        }
+        if (my $wcb = delete $env->{'qspawn.wcb'}) {
                 # have we started writing, yet?
                 require PublicInbox::WwwStatic;
                 $wcb->(PublicInbox::WwwStatic::r(500));
diff --git a/lib/PublicInbox/SolverGit.pm b/lib/PublicInbox/SolverGit.pm
index d3567aa2..dbb9b739 100644
--- a/lib/PublicInbox/SolverGit.pm
+++ b/lib/PublicInbox/SolverGit.pm
@@ -242,10 +242,8 @@ sub find_smsgs ($$$) {
 
 sub update_index_result ($$) {
         my ($bref, $self) = @_;
-        my ($qsp, $msg) = delete @$self{qw(-qsp -msg)};
-        if (my $err = $qsp->{err}) {
-                ERR($self, "git update-index error: $err");
-        }
+        my ($qsp_err, $msg) = delete @$self{qw(-qsp_err -msg)};
+        ERR($self, "git update-index error:$qsp_err") if $qsp_err;
         dbg($self, $msg);
         next_step($self); # onto do_git_apply
 }
@@ -278,7 +276,7 @@ sub prepare_index ($) {
         my $cmd = [ qw(git update-index -z --index-info) ];
         my $qsp = PublicInbox::Qspawn->new($cmd, $self->{git_env}, $rdr);
         $path_a = git_quote($path_a);
-        $self->{-qsp} = $qsp;
+        $qsp->{qsp_err} = \($self->{-qsp_err} = '');
         $self->{-msg} = "index prepared:\n$mode_a $oid_full\t$path_a";
         $qsp->psgi_qx($self->{psgi_env}, undef, \&update_index_result, $self);
 }
@@ -405,10 +403,8 @@ sub mark_found ($$$) {
 
 sub parse_ls_files ($$) {
         my ($self, $bref) = @_;
-        my ($qsp, $di) = delete @$self{qw(-qsp -cur_di)};
-        if (my $err = $qsp->{err}) {
-                die "git ls-files error: $err";
-        }
+        my ($qsp_err, $di) = delete @$self{qw(-qsp_err -cur_di)};
+        die "git ls-files error:$qsp_err" if $qsp_err;
 
         my ($line, @extra) = split(/\0/, $$bref);
         scalar(@extra) and die "BUG: extra files in index: <",
@@ -456,11 +452,11 @@ sub skip_identical ($$$) {
 
 sub apply_result ($$) {
         my ($bref, $self) = @_;
-        my ($qsp, $di) = delete @$self{qw(-qsp -cur_di)};
+        my ($qsp_err, $di) = delete @$self{qw(-qsp_err -cur_di)};
         dbg($self, $$bref);
         my $patches = $self->{patches};
-        if (my $err = $qsp->{err}) {
-                my $msg = "git apply error: $err";
+        if ($qsp_err) {
+                my $msg = "git apply error:$qsp_err";
                 my $nxt = $patches->[0];
                 if ($nxt && oids_same_ish($nxt->{oid_b}, $di->{oid_b})) {
                         dbg($self, $msg);
@@ -474,9 +470,9 @@ sub apply_result ($$) {
         }
 
         my @cmd = qw(git ls-files -s -z);
-        $qsp = PublicInbox::Qspawn->new(\@cmd, $self->{git_env});
+        my $qsp = PublicInbox::Qspawn->new(\@cmd, $self->{git_env});
         $self->{-cur_di} = $di;
-        $self->{-qsp} = $qsp;
+        $qsp->{qsp_err} = \($self->{-qsp_err} = '');
         $qsp->psgi_qx($self->{psgi_env}, undef, \&ls_files_result, $self);
 }
 
@@ -508,7 +504,7 @@ sub do_git_apply ($) {
         my $opt = { 2 => 1, -C => $dn, quiet => 1 };
         my $qsp = PublicInbox::Qspawn->new(\@cmd, $self->{git_env}, $opt);
         $self->{-cur_di} = $di;
-        $self->{-qsp} = $qsp;
+        $qsp->{qsp_err} = \($self->{-qsp_err} = '');
         $qsp->psgi_qx($self->{psgi_env}, undef, \&apply_result, $self);
 }
 
@@ -660,7 +656,7 @@ sub new {
                 gits => $ibx->{-repo_objs},
                 user_cb => $user_cb,
                 uarg => $uarg,
-                # -cur_di, -qsp, -msg => temporary fields for Qspawn callbacks
+                # -cur_di, -qsp_err, -msg => temp fields for Qspawn callbacks
 
                 # TODO: config option for searching related inboxes
                 inboxes => [ $ibx ],
diff --git a/lib/PublicInbox/ViewVCS.pm b/lib/PublicInbox/ViewVCS.pm
index 3cbc363b..d3fd152d 100644
--- a/lib/PublicInbox/ViewVCS.pm
+++ b/lib/PublicInbox/ViewVCS.pm
@@ -1,4 +1,4 @@
-# Copyright (C) 2019-2021 all contributors <meta@public-inbox.org>
+# Copyright (C) all contributors <meta@public-inbox.org>
 # License: AGPL-3.0+ <https://www.gnu.org/licenses/agpl-3.0.txt>
 
 # show any VCS object, similar to "git show"
@@ -76,10 +76,9 @@ sub stream_large_blob ($$$$) {
 
 sub show_other_result ($$) {
         my ($bref, $ctx) = @_;
-        my ($qsp, $logref) = delete @$ctx{qw(-qsp -logref)};
-        if (my $err = $qsp->{err}) {
-                utf8::decode($$err);
-                $$logref .= "git show error: $err";
+        my ($qsp_err, $logref) = delete @$ctx{qw(-qsp_err -logref)};
+        if ($qsp_err) {
+                $$logref .= "git show error:$qsp_err";
                 return html_page($ctx, 500, $logref);
         }
         my $l = PublicInbox::Linkify->new;
@@ -99,10 +98,9 @@ sub show_other ($$$$) {
         my $cmd = ['git', "--git-dir=$git->{git_dir}",
                 qw(show --encoding=UTF-8 --no-color --no-abbrev), $oid ];
         my $qsp = PublicInbox::Qspawn->new($cmd);
-        my $env = $ctx->{env};
-        $ctx->{-qsp} = $qsp;
+        $qsp->{qsp_err} = \($ctx->{-qsp_err} = '');
         $ctx->{-logref} = $logref;
-        $qsp->psgi_qx($env, undef, \&show_other_result, $ctx);
+        $qsp->psgi_qx($ctx->{env}, undef, \&show_other_result, $ctx);
 }
 
 # user_cb for SolverGit, called as: user_cb->($result_or_error, $uarg)