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https://issues.apache.org/jira/browse/CASSANDRA-21381?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=18084210#comment-18084210
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Jens Geyer edited comment on CASSANDRA-21381 at 5/28/26 9:07 PM:
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{quote}CSV format as standardized and defined in RFC 4180 doesn't support
control characters. It excludes them by omission in the BNF, defining TEXTDATA
as only printable characters:
{quote}
As I see it, that leaves at least two options:
# CSV in the Cassandra context stands for "Cassandra Serialized Values"
nothing else was ever intended and the RFC surely cannot be applied ;)
# Keep current meaning, document the RFC-implied limitations and redirect
people to using `sstabledump` and `sstableloader` instead
was (Author: jensg):
{quote}CSV format as standardized and defined in RFC 4180 doesn't support
control characters. It excludes them by omission in the BNF, defining TEXTDATA
as only printable characters:{quote}
As I see it, that leaves at least two options:
# Explain CSV in the Cassandra context stands for "Cassandra Serialized
Values", nothing else was ever intended and the RFC surely cannot be applied ;-)
# Keep current meaning, document the RFC-implied limitations and redirect
people to using `sstabledump` and `sstableloader` instead
> CSV COPY TO corrupts control characters (newline, null byte, etc.) in text
> values
> ---------------------------------------------------------------------------------
>
> Key: CASSANDRA-21381
> URL: https://issues.apache.org/jira/browse/CASSANDRA-21381
> Project: Apache Cassandra
> Issue Type: Bug
> Components: CQL/Interpreter
> Reporter: Jens Geyer
> Assignee: Arvind Kandpal
> Priority: Normal
> Time Spent: 2h
> Remaining Estimate: 0h
>
> h2. Problem
> During COPY TO, control characters in text column values are replaced with
> their Python repr() notation by
> UNICODE_CONTROLCHARS_RE.sub(_show_control_chars, ...) in
> {{format_value_text}} ({{pylib/cqlshlib/formatting.py}}).
> Examples:
> * A stored newline (0x0A) becomes the two-character sequence {{\n}} in the
> CSV; after COPY FROM it is stored as {{\n}} (backslash + n) -- a different
> value.
> * A null byte (0x00) becomes {{\x00}} (six characters).
> The regex {{UNICODE_CONTROLCHARS_RE = re.compile(r"[\x00-\x1f\x7f-\xa0]")}}
> matches all ASCII control characters (0x00-0x1F: newline, tab, carriage
> return, BEL, etc.) and Latin-1 supplement control characters (0x7F-0xA0).
> This substitution is correct for terminal display of SELECT results (where
> invisible characters need a human-readable representation). It is incorrect
> in the *CSV export path*, where {{csv.writer}} handles control characters
> correctly via field quoting -- no pre-processing is needed.
> h2. Affected Versions
> All Cassandra versions with {{format_value_text}} containing the
> {{UNICODE_CONTROLCHARS_RE}} substitution (at minimum 3.x through trunk).
> h2. Root Cause
> {{format_value_text}} is shared between the terminal display path (SELECT
> output) and the CSV export path (COPY TO). The {{UNICODE_CONTROLCHARS_RE}}
> substitution converts control characters to their Python repr-string for
> display, but this transformation is *not reversible* via the CSV import path.
> This bug is *independent of, but in the same function as*, the
> backslash-doubling bug fixed in CASSANDRA-21131. Applying the CASSANDRA-21131
> patch does NOT fix this issue.
> h2. Expected Fix
> In the CSV export path, skip the {{UNICODE_CONTROLCHARS_RE.sub(...)}} call.
> An {{escape_control_chars}} parameter (analogous to the {{escape_backslash}}
> parameter introduced by CASSANDRA-21131) can conditionally suppress the
> substitution when calling {{format_value_text}} from the CSV export path.
> h2. Related
> CASSANDRA-21131 -- backslash-doubling bug in the same code path, already
> patched.
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