Question

Can someone explain what’s happening here?
It seems that the placeholding syntax in SQL statement string doesn’t work as expected (or, to say it in a different way, it violates the principle of least surprise), and during runtime an unexpected substitution/escaping is done for var2:

ruby-1.9.2-p290 :001 > puts RUBY_VERSION
1.9.2
 => nil 

ruby-1.9.2-p290 :002 > require 'ipaddr'
=> true 

ruby-1.9.2-p290 :003 > require 'sqlite3'
=> true 

ruby-1.9.2-p290 :004 > var1 = Addrinfo.ip("1.2.3.4")
=> #<Addrinfo: 1.2.3.4> 

ruby-1.9.2-p290 :005 > var2 = var1.ip_address
=> "1.2.3.4" 

ruby-1.9.2-p290 :006 > var3 = "1.2.3.4"
=> "1.2.3.4" 

ruby-1.9.2-p290 :007 > var2 == var3
=> true

ruby-1.9.2-p290 :008 > var2 === var3
=> true

ruby-1.9.2-p290 :009 > var2.eql?(var3)
=> true 

ruby-1.9.2-p290 :010 > db = SQLite3::Database.open( "test.db" )
=> #<SQLite3::Database:0x00000100bcfce0>

ruby-1.9.2-p290 :011 > db.execute( "SELECT * FROM devices WHERE deviceaddr=?", var2 )
=> [] 

ruby-1.9.2-p290 :011 > db.execute( "SELECT * FROM devices WHERE deviceaddr=?", var2.to_s )
=> [] 

ruby-1.9.2-p290 :012 > db.execute( "SELECT * FROM devices WHERE deviceaddr=?", var3 )
=> [["TEST_DEVICE", "1.2.3.4"]] 

Without the SQL placeholder it works (but exposes the db to SQL injections!):

ruby-1.9.2-p290 :013 > db.execute( "SELECT * FROM devices WHERE deviceaddr='#{var2}'" )
=> [["TEST_DEVICE", "1.2.3.4"]] 

So what is a safe way to make this work?

Answer 1

TL;DR: SQLite uses UTF; convert Addrinfo’s 8-bit ASCII output.

One “safe” way is to use force_encoding("UTF-8") on the output from Addrinfo, so:

> var1.ip_address.encoding
 => #<Encoding:ASCII-8BIT> 
> var3.encoding
 => #<Encoding:UTF-8> 
> db.execute("SELECT * FROM foo WHERE ip=?", var2.force_encoding("UTF-8"))
 => [["1.2.3.4"]]