On 2023-03-07 11:53:29 +0100, Mathias Mayrhofer wrote: > I came across the "bytea_output" configuration variable inside postgresql.conf. > It seems to be affecting the "digest" function, but in a way I cannot > understand. No, it just affects the way bytea values are displayed. The return value of the digest() function is a 32 byte bytea value in both cases. But you can choose wether you want to display bytea values as 2 hex digits per byte or as a mixture of printable ascii characters and octal escapes. > When my postgresql 14 server executes the digest function, it considers the > "bytea_output" variable, but the output of the function is *NOT* the same as > the "encode" function. It differs only slightly. I don't think the docs say anywhere that these are the same. In particular, https://www.postgresql.org/docs/15/datatype-binary.html#id-1.5.7.12.9 says that "the entire string is preceded by the sequence \x (to distinguish it from the escape format". > -- /etc/postgresql/14/main/postgresql.conf > -- bytea_output = 'escape' > > db=> select encode(digest('mtmayr', 'sha256'), 'escape'); > ┌────────────────────────────────────────────────────────────────────────────────────────────┐ > │ encode │ > ├────────────────────────────────────────────────────────────────────────────────────────────┤ > │ \277\x19\225\335g\307\224\337-\347Y\203\254\324\x1Ff\307Ph*\267\\\243\2515S\213WX\204\375G │ > └────────────────────────────────────────────────────────────────────────────────────────────┘ This is a bit weirder. Why are there two bytes encoded as hex instead of octal? It turns out this is again an artefact of displaying the value. https://www.postgresql.org/docs/14/functions-binarystring.html says: | The escape format converts zero bytes and bytes with the high bit set | into octal escape sequences (\nnn), and it doubles backslashes. Other | byte values are represented literally. So the byte 0x19 is converted to a single character U+0019 (EM) which is then displayed as '\x19', while bytes >= 0x80 are converted to four-character escape sequences. hp -- _ | Peter J. Holzer | Story must make more sense than reality. |_|_) | | | | | hjp@xxxxxx | -- Charles Stross, "Creative writing __/ | http://www.hjp.at/ | challenge!"
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