net: panic: runtime error: invalid memory address or nil pointer dereference

[sylr]

What version of Go are you using (go version)?

$ go version 1.13.5

Does this issue reproduce with the latest release?

What operating system and processor architecture are you using (go env)?

go env Output

$ go env

What did you do?

I've a traefik reverse proxy which panics a lot:

panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x18 pc=0x58768f]
goroutine 6594 [running]:
bufio.(*Writer).Available(...)
	/usr/local/go/src/bufio/bufio.go:610
bufio.(*Writer).WriteString(0x0, 0x255bbf4, 0x19, 0xc002ab8300, 0x40919b, 0xc00003a000)
	/usr/local/go/src/bufio/bufio.go:691 +0x7f
net/http.(*expectContinueReader).Read(0xc00099fd20, 0xc002ab8300, 0x67a, 0x67a, 0x1ff03a0, 0xc002bc5001, 0xc002ab8300)
	/usr/local/go/src/net/http/server.go:888 +0x13b
io.(*LimitedReader).Read(0xc000655e80, 0xc002ab8300, 0x67a, 0x67a, 0x0, 0xc00140b800, 0x40a1b8)
	/usr/local/go/src/io/io.go:448 +0x63
io.copyBuffer(0x2958c40, 0xc0006e9a00, 0x2955200, 0xc000655e80, 0xc002ab8300, 0x67a, 0x67a, 0x5, 0xc00140b9b0, 0x5)
	/usr/local/go/src/io/io.go:402 +0x122
io.Copy(...)
	/usr/local/go/src/io/io.go:364
net.genericReadFrom(0x2955c40, 0xc001200428, 0x2955200, 0xc000655e80, 0x0, 0x0, 0x245a600)
	/usr/local/go/src/net/net.go:625 +0x9a
net.(*TCPConn).readFrom(0xc001200428, 0x2955200, 0xc000655e80, 0xc00140b9e8, 0x40a48a, 0x21495c0)
	/usr/local/go/src/net/tcpsock_posix.go:54 +0xe2
net.(*TCPConn).ReadFrom(0xc001200428, 0x2955200, 0xc000655e80, 0x7f2c616def88, 0xc001200428, 0x1)
	/usr/local/go/src/net/tcpsock.go:103 +0x4d
io.copyBuffer(0x2955c40, 0xc001200428, 0x2955200, 0xc000655e80, 0x0, 0x0, 0x0, 0x2247760, 0x7f2c616dee01, 0x7f2c616def68)
	/usr/local/go/src/io/io.go:388 +0x2ed
io.Copy(...)
	/usr/local/go/src/io/io.go:364
net/http.persistConnWriter.ReadFrom(0xc00190aea0, 0x2955200, 0xc000655e80, 0x7f2c616def68, 0xc00190aea0, 0x1)
	/usr/local/go/src/net/http/transport.go:1599 +0x85
bufio.(*Writer).ReadFrom(0xc001f10440, 0x2955200, 0xc000655e80, 0x7f2c616def48, 0xc001f10440, 0x1)
	/usr/local/go/src/bufio/bufio.go:713 +0x34a
io.copyBuffer(0x29519e0, 0xc001f10440, 0x2955200, 0xc000655e80, 0x0, 0x0, 0x0, 0xc00140bc38, 0x40cb78, 0x20)
	/usr/local/go/src/io/io.go:388 +0x2ed
io.Copy(...)
	/usr/local/go/src/io/io.go:364
net/http.(*transferWriter).doBodyCopy(0xc000aa7540, 0x29519e0, 0xc001f10440, 0x2955200, 0xc000655e80, 0x0, 0xc00140bee0, 0xc003463b80)
	/usr/local/go/src/net/http/transfer.go:400 +0x6a
net/http.(*transferWriter).writeBody(0xc000aa7540, 0x29519e0, 0xc001f10440, 0x2, 0x2)
	/usr/local/go/src/net/http/transfer.go:359 +0x6da
net/http.(*Request).write(0xc0015d1e00, 0x29519e0, 0xc001f10440, 0x0, 0xc001ed8f60, 0xc00099ff60, 0x0, 0x0)
	/usr/local/go/src/net/http/request.go:682 +0x6d3
net/http.(*persistConn).writeLoop(0xc00190aea0)
	/usr/local/go/src/net/http/transport.go:2207 +0x1c8
created by net/http.(*Transport).dialConn
	/usr/local/go/src/net/http/transport.go:1575 +0xb23

I've failed to identified the client behaviour/request that provokes this.

[mvdan]

It sounds like you should file this bug with traefik, not here. This is a very common panic that can happen with certain kinds of bugs in people's code.