get rid of some panics (#1526)

* client: simplify (*HostClient).do()

Remove an allocation in favour of deferring a call to release the
response.

* client: remove panic in dialAddr

Return an error instead of panicking if the user supplied a nonsensical
DialFunc.

* compression: remove panic on invalid compression level

If a compression level exceeding gzip's boundaries is provided, fasthttp
will panic. Instead it would be better to handle this error for them by
limiting it to the minimum or maximum value, depending on the direction
the user has exceeded the limits.

Clamp the value of gzip to always be between gzip.BestSpeed and
gzip.BestCompression.

* peripconn: remove panic on negative connection count

When a negative count is reached when unregistering a connection, a
panic is caused even though data-integrity is not at risk.

Replace the panic() with a simple clamp on the value to ensure the
value does not exceed it's expected lower bounds.

References: #1504

* compress: remove error on failed nonblocking writes

Since there is no way of handling or even logging non-critical errors in
stateless non-blocking writecalls, just drop them and hope the user
notices and tries again.

* workerPool: remove panic on redundant Start and Stop calls

Instead of panicking for invalid behaviour, it's preferable to just turn
the function into a noop.

* http: remove panic on invalid form boundary

* http: remove panic on negative reads

Since bufio already panics on negative reads, it is not necessary to do
so as well. If the length is zero and for some reason no error is
returned, readBodyIdentity and appendBodyFixedSize now errors in these
cases.

Link: https://github.com/golang/go/blob/851f6fd61425c810959c7ab51e6dc86f8a63c970/src/bufio/bufio.go#L246

* fs: remove panic on negative reader count

When a negative count is reached when unregistering a reader, a panic is
thrown even though data-integrity is not at risk.

Replace the panic() with a simple clamp on the value to ensure the
value does not exceed it's expected lower bounds.

* server: remove panic in favour of a segfault

Panicking with "BUG: " obscures the error. As the segfault causes a
panic anyway, just let the chaos unfold.

* server: remove panic in favour of returning an error

Writing on a timed-out response is not endangering data integrity and
just fails.

* chore: add comments to all panics

* chore: fix minor typo

1 files changed, 3 insertions, 0 deletions

diff --git a/bytesconv.go b/bytesconv.go
index 9b2ffeb..809b490 100644
--- a/bytesconv.go
+++ b/bytesconv.go
@@ -79,6 +79,7 @@ func ParseIPv4(dst net.IP, ipStr []byte) (net.IP, error) {
 	copy(dst, net.IPv4zero)
 	dst = dst.To4()
 	if dst == nil {
+		// developer sanity-check
 		panic("BUG: dst must not be nil")
 	}
 
@@ -126,6 +127,7 @@ func ParseHTTPDate(date []byte) (time.Time, error) {
 // AppendUint appends n to dst and returns the extended dst.
 func AppendUint(dst []byte, n int) []byte {
 	if n < 0 {
+		// developer sanity-check
 		panic("BUG: int must be positive")
 	}
 
@@ -281,6 +283,7 @@ var hexIntBufPool sync.Pool
 
 func writeHexInt(w *bufio.Writer, n int) error {
 	if n < 0 {
+		// developer sanity-check
 		panic("BUG: int must be positive")
 	}