Process hangs in query block if doing rs.read before rs.each

[samueleaton]

(From our chat in gitter.im)

Process stops at a rs.read(String) for minutes without ever continuing (chk 2 will never be printed):

db.query query_str, var1, var2 do |rs|
  puts "chk 1"
  something = rs.read(String)
  puts "chk 2"
end

The following examples work fine:

# using query_one
db.query_one query_str, var1, var2 do |rs|
  something = rs.read(String)
end

# using from_rs via DB.mapping
db.query query_str, var1, var2 do |rs|
  from_rs rs
end

# using rs.each
db.query query_str, var1, var2 do |rs|
  rs.each do
    something = rs.read(String)
  end
end

Although I was not using the API correctly, an exception should be raised.

Using pg driver

[RX14]

The same happens if you try to rs.read when there isn't another column. Basically unless you do it perfectly, you get hangs instead of exceptions. I spent quite a while debugging this! This might be limited to the PG driver only. @will?

[samueleaton]

See our conversation in gitter here: https://gitter.im/crystal-lang/crystal/archives/2017/01/13

[samueleaton]

From our conversion that I posted to, @spalladino said:

Even if it works, please open an issue in crystal-db explaining the situation; if making that check does not incur in a performance penalty, I'd consider adding it to raise an exception rather than just hanging on the socket