tx/textual/valuerenderer: should formatInteger return "0" for an empty string "" instead of crashing?

[odeke-em]

Summary of Bug

While auditing the code in TX_SIGNMODE_TEXTUAL, I read through the code in

cosmos-sdk/tx/textual/valuerenderer/int.go

Lines 32 to 33 in ccc8003

	func formatInteger(v string) (string, error) {
	if v[0] == '-' {

which assumes the first leading digits will always be non-empty and confirmed alas that if one passes in the variants of a valid decimal string like ".99" or "10.", the former crashes with

$ go test -run=FormatxDecimal -v
=== RUN   TestFormatxDecimal
Callers: /Users/emmanuelodeke/go/src/go.googlesource.com/go/src/testing/testing.go:1446
Parts: []string{"", "10"}
--- FAIL: TestFormatxDecimal (0.00s)
panic: runtime error: index out of range [0] with length 0 [recovered]
	panic: runtime error: index out of range [0] with length 0

goroutine 19 [running]:
testing.tRunner.func1.2({0x1446b60, 0xc0000d0288})
	/Users/emmanuelodeke/go/src/go.googlesource.com/go/src/testing/testing.go:1396 +0x24e
testing.tRunner.func1()
	/Users/emmanuelodeke/go/src/go.googlesource.com/go/src/testing/testing.go:1399 +0x39f
panic({0x1446b60, 0xc0000d0288})
	/Users/emmanuelodeke/go/src/go.googlesource.com/go/src/runtime/panic.go:884 +0x212
cosmossdk.io/tx/textual/valuerenderer.formatInteger({0x1470b3a?, 0xc0000ba008?})
	/Users/emmanuelodeke/go/src/github.com/cosmos/cosmos-sdk/tx/textual/valuerenderer/int.go:33 +0xef
cosmossdk.io/tx/textual/valuerenderer.formatDecimal({0x1470b3a, 0x3})
	/Users/emmanuelodeke/go/src/github.com/cosmos/cosmos-sdk/tx/textual/valuerenderer/dec.go:41 +0x16c
cosmossdk.io/tx/textual/valuerenderer.TestFormatxDecimal(0xc00017a000)
	/Users/emmanuelodeke/go/src/github.com/cosmos/cosmos-sdk/tx/textual/valuerenderer/dec_test.go:6 +0x31
testing.tRunner(0xc00017a000, 0x14a6280)
	/Users/emmanuelodeke/go/src/go.googlesource.com/go/src/testing/testing.go:1446 +0x10b
created by testing.(*T).Run
	/Users/emmanuelodeke/go/src/go.googlesource.com/go/src/testing/testing.go:1493 +0x35f
exit status 2
FAIL	cosmossdk.io/tx/textual/valuerenderer	0.219s

Version

ccc8003

Steps to Reproduce

package valuerenderer

import "testing"
        
func TestFormatxDecimal(t *testing.T) {
        s, err := formatDecimal(".10")
        if err != nil {
                t.Fatal(err)
        }
        if g, w := s, "0.10"; g != w {
                t.Errorf("got =%q\nwant=%q", g, w)
        }
}

and the question is, should we support "" and return "0" so that ".99" can work just the way "10." works? Fuzzers will also flag this.

Kindly cc-ing @AmauryM @marbar3778.

[tac0turtle]

@AmauryM @facundomedica is this still an issue?

[amaury1093]

Yes, probably an edge case that's good to be fixed. I'll add it to the Textual tracking issue.

[facundomedica]

• Passing any of: .99, 1., ., "empty" as amounts in the coin tests results in decimal string cannot be empty or invalid decimal length
• Passing an empty string to the integer renderers returns invalid syntax

So no crashes now 👍