database/sql: ColumnConverter is bypassed when NumInput returns -1

[flimzy]

Go version

go version go1.22.0 linux/amd64

Output of go env in your module/workspace:

GO111MODULE=''
GOARCH='amd64'
GOBIN=''
GOCACHE='/home/jonhall/.cache/go-build'
GOENV='/home/jonhall/.config/go/env'
GOEXE=''
GOEXPERIMENT=''
GOFLAGS=''
GOHOSTARCH='amd64'
GOHOSTOS='linux'
GOINSECURE=''
GOMODCACHE='/home/jonhall/go/pkg/mod'
GONOPROXY='gitlab.com/FlashbackSRS/priv,gitlab.com/flimzy/hacker-portfolio'
GONOSUMDB='gitlab.com/FlashbackSRS/priv,gitlab.com/flimzy/hacker-portfolio'
GOOS='linux'
GOPATH='/home/jonhall/go'
GOPRIVATE='gitlab.com/FlashbackSRS/priv,gitlab.com/flimzy/hacker-portfolio'
GOPROXY='https://proxy.golang.org,direct'
GOROOT='/usr/local/go'
GOSUMDB='sum.golang.org'
GOTMPDIR=''
GOTOOLCHAIN='auto'
GOTOOLDIR='/usr/local/go/pkg/tool/linux_amd64'
GOVCS=''
GOVERSION='go1.22.0'
GCCGO='/usr/bin/gccgo'
GOAMD64='v1'
AR='ar'
CC='gcc'
CXX='g++'
CGO_ENABLED='1'
GOMOD='/home/jonhall/src/bugrepro/go.mod'
GOWORK=''
CGO_CFLAGS='-w'
CGO_CPPFLAGS=''
CGO_CXXFLAGS='-O2 -g'
CGO_FFLAGS='-O2 -g'
CGO_LDFLAGS='-O2 -g'
PKG_CONFIG='pkg-config'
GOGCCFLAGS='-fPIC -m64 -pthread -Wl,--no-gc-sections -fmessage-length=0 -ffile-prefix-map=/tmp/go-build1095939242=/tmp/go-build -gno-record-gcc-switches'

What did you do?

I wrote a database/sql driver that implements the optional ColumnConverter interface for prepared statements, and for which NumInputs() returns -1.

Technically, I wrote a databse/sql proxy driver, for the purpose of adding hooks to DB operations, to aide in debugging. See https://gitlab.com/flimzy/errsql

But using this library with modernc.org/sqlite is what triggered the buggy behavior. modernc.org/sqlite itself does not implement the ColumnConverter interface, but it does return -1 for NumInputs. Because the proxy driver does implement ColumnConverter (because it must implement it for all drivers it proxies, or none), it triggers the observed behavior.

What did you see happen?

The ColumnConverter method is never called, leading to the following error from sqlite:

invalid driver.Value type int

What did you expect to see?

I expected that ColumnConverter would be called.

Analysis & Possible Fix

This line appears to be the culprit:

	if c.want <= index {

c.want is set to the return value from stmt.NumInputs(), so is -1 in this case. The method containing this code is only executed when ColumnConverter is implemented, as we can see here.

I believe the solution is to change the above mentioned line to:

	if c.want > 0 && c.want <= index {

[gopherbot]

Change https://go.dev/cl/597115 mentions this issue: database/sql: Don't skip default argument conversion for ColumnConverters and unknown input count

[thanm]

@bradfitz @kardianos per owners.

[thanm]

Thanks for sending a CL --

[gabyhelp]

Related Issues and Documentation

• database/sql: fallback to default argument conversion fails when ColumnConverter is implemented #68344 (closed)
• Proposal: database/sql: NULL column values should be parsed as zero values for floats and ints instead of trying to parse with strconv #22542 (closed)

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