serve: every failure inside _serve_handle is dropped with no record, so a server bug is wire-identical to a client disconnect

[sotashimozono]

_serve_handle wraps its whole body in an untargeted handler:

catch e
    e isa InterruptException && rethrow()
    return nothing                                    # client closed / malformed: drop it
finally
    close(conn)
end

The comment names the case it was written for — a client that hung up. But it catches everything, and the two are indistinguishable afterwards, on the wire and in the log.

Measured

Against a live Pinax.serve on 73f2f77, one raw socket per request, stdout and stderr captured around each:

request	bytes received	server output
GET /data.bin (control)	1146	—
GET /empty.bin + Range: bytes=0-0	0	nothing
GET /data.bin + Range: bytes=999999999999999999999999-1	0	nothing

Both zero-byte rows are real exceptions — a BoundsError from data[1:1] on an empty vector, and an OverflowError from parse(Int, …). Neither is logged anywhere. A client sees exactly what it sees when it disconnects first: a closed socket.

Why this is separate from #108

#108 is the arithmetic: the suffix-range misreading and the empty-file slice. Fixing it removes these two inputs. It does not change what happens to the next exception in this block — a SystemError from a file that is unlinked between isfile and read, an OutOfMemoryError on a large asset, a bug introduced by a later edit. Each of those will also close the connection silently.

The asymmetry inside the same file is the tell: serve prints its URL, warns when the directory has no index.html, and answers a missing path with 404 Not Found: <rel> — it is not a quiet component by design. Only the failure path is quiet.

Fix

Log before discarding, and keep discarding:

catch e
    e isa InterruptException && rethrow()
    e isa Base.IOError || @error "Pinax.serve: request failed" exception=(e, catch_backtrace()) target=rel
    return nothing
finally
    close(conn)
end

IOError is the genuine hung-up-client case and stays silent; everything else says so once. The 403 containment branch is worth the same treatment — it currently blocks a request without recording which one.